There are four "formats" for encoding files posted to Usenet - UUEncode, Binhex, XXE, and Base64 (MIME). While many news readers can handle most, if not all, of these, you may find yourself with a file that won't decode in yours.  The below is a list of Decoders that you may need to add to your system in order to decode them. Configure your decoder to join multiparts (concatenate).  Occasionally, a Usenet poster will bundle several files into one MIME post (not in ABME, please!!!) and a good decoder will extract all of them if configured correctly.  Here are some shareware decoders to try out:

• XferPro Shareware: from Sabasoft (Windows and Macintosh) Just double click on any file you want to decode.  XferPro will create the new file with the correct filename in the same directory and then close by itself.  If the file size says 0, not to worry.  That will right itself after refreshing the view or using the file.  Try to open the book or extract the zip file you just decoded.  If all goes well, delete the encoded file(s).
  
  
• Decode Shell Extension - This Windows Extension utility adds a choice to the Windows Contextual menu ( the menu that appears when you right click on a window, link, or icon) that will allow you to manually decode a UUEncoded, Binhex, XXE, or Base64(MIME) file that you have saved manually.  Great for dealing with those pesky Base64 files that won't seem to open or decode.  Plus, it's free.
  
  
• MindExpander - free from MindVision, the very same company that created the Installer VISE installer utility used by programmers that you have undoubtedly been exposed to no fewer than a thousand times as you've installed new software. MindExpander has become popular due to its ability to effortlessly handle .SIT, .SEA, .HQX, .BIN, and .ZIP.  It's definitely worth a download, for both Windows and Macintosh

Avoid viruses by not downloading any executables from ABEB (.exe, .com, .dll or .bat files, or zip archives containing them). 
First of all, they don't belong there, and in the Links are URLs for reliable download sites for all the recommended software. Invariably, the safest places to download from are the author's web or ftp site, or major archive sites.  Second best are other reputable host sites. The LEAST desirable are Usenet newsgroups.

A zip archive can contain anything, including executables. You can't go strictly by what the Usenet subject header says. Get a zip extraction utility with a graphical user interface, such as WinZip, and learn what all the commands do. For instance, don't assume you know what "check out" means. You can safely decompress the contents of the zip archive, but don't run any of the executable files until you've performed a virus scan on them. If a virus is present, the only way you could activate it is by executing the file.

Zip

Zip files are file(s) compressed using pkzip, one of the simplest to use forms of compressed files. In use with media files, the compression factor is almost nil, running most normally around 4 or 5%.  The advantage cited most often to zip is that it allows multiple files to be placed within the single zip file, and often in ABME the zip file will have a password protecting the media file itself, preventing accidental viewing of adult material by minors (or clueless newbies ).  This extra level of protection (for the poster, especially!) was referred to when the U.S. Congress was exploring the Internet before drafting the Communications Decency Act. They cited the use of these passwords as Usenet's "making an effort" to protect against accidental viewing.  The debate over passwords continues with no consensus, although it always comes down to being the poster's prerogative.

A password may be contained in a text file that is also inside the zip file.

1. Open the zip file using Winzip in Classic Mode (or another GUI extraction utility).  You should see that it contains two files.  One is the book which will have a plus sign (+) by its filename, indicating that it is password protected.  The other file will be an unprotected text file containing a message for you as well as the required password.

2. Highlight the text file and click View.  After you read the text file and get the password,

3. Highlight the password protected file.  Click on Extract.  You will be prompted to enter the password, which is case sensitive.

4. Type it exactly the way it was shown in the text file, or paste it in.

5. Click and you're done.

In Dos, using PKUnzip.exe, you will receive an error message, but the text file will be uncompressed. Read it for the password, then run the unzip command again using the -s switch.

On a Mac, try using UnZip 5.32.

RAR

Rar: xxxx.r01, xxxx.r02. This file type is the most common USENET method of breaking down large files for posting on the net.  Used heavily in alt.binaries.e-book, alt.binaries.cdimage, and other large file groups, Rar developed as the best means of posting 100 meg plus files.  With the almost absolute certainty that files of this size would not make it complete to other servers, Rar breaks down the large file(s) into multiple smaller files, allowing the poster to repost the parts that didn't reach those downloading.  Like Zip files, the compression factor of Rar on media files is almost nil. Most references that follow refer to WinRar, but WinAce works in much the same way.

Elements of a RAR post:

A file named BOOK.TXT becomes BOOK.r00, BOOK.r01, BOOK.r02, etc. For files with more than 100 parts, the file after "r99" becomes ".s00", then ".s01", and on.

Depending on the compression system being used, there may be a BOOK.rar or BOOK.exe (self-extracting) file also created.

Better posters will also include a BOOK.nfo or 0/xxx file which contains the information about how many parts, and many un-rar-ing software systems can use this file to confirm that all parts are complete and uncorrupted.

How to

1. First, make sure you have obtained all the parts of the Rar'ed file.  The poster should have included this information within the the header [ BOOK.TXT {info, info} (04/40) -- BOOK.r04 ] This means you should have 40 or 41 ( BOOK.r00 ) parts. DO NOT confuse the parts of a Rar file with the Parts as posted to Usenet.  BOOK.r04 may be 10,000 lines posted to Usenet in 10 line parts!  Meaning you must first collect all 10 parts of BOOK.r04 - BOOK.r04 (1/10), BOOK.r04 (2/10), etc.  A good news reader should do this part for you. You are using one of the suggested readers...right?

2. Use a Rar utility to assemble the sections, recombining them into the completed file.  RAR - UnRAR, WinRAR or MacUnRAR, archive sites.

3. Once you've installed it, you should be able to join rar by clicking on the xxx.rar section, which will start your Rar program.

There is one other type of Rar file that needs to be mentioned, and that is the self extracting Rar file. This version has the above file structure, but also includes an ".exe" part with the file name before it.
To join this type:

1. Follow step one above, and include the ".exe" section when downloading.
2. Run a virus check on all of it.
3. Click on the ".exe" file, and it will self extract the book from the parts.

If you're still having problems, check out the WinRar Beginners Help page.

Ace

Every once and awhile, just to make sure the faqs are alive and well, someone throws a new diddie into the mix, and ace files are just that. Ace is the same type as rar, and all the rar stuff applys, but ace files are the compression / division scheme of ... tada "WinAce".com, not "WinRar.com" or "WinZip.com". Damn, I bet you wish you'd thought of that before reading this rant.

Other Compression Types

Here are the file types to watch for and where to find the required decompression software.

ZIP
WinZip or for the MAC UnZip 5.32 or PowerArchiver or... (you get the idea)
The most common form of compression used to date.

RAR
WinRar or MacRAR
RAR is the second most used compression system on Usenet. It may be shareware but it generally yields higher compression ratios (smaller files) than the zip algorithm.

ACE
WinAce
Offers very high compression ratios as well - sometimes higher than those offered by ZIP or RAR.
Note: there is a new beta version which creates archives that older WinAce versions cannot open. Winrar also will not open the new archives.

TAR.GZ
This is the extension of a TApe Archive that has been Gnu-Zipped. Commonly referred to as a "tarball", this extension is universal within the Unix/Linux world, and has been around a *very* long time. (It's one of the oldest forms of compression used.) You should be able to use WinZip to open them w/out much trouble.

TGZ
This is the same as a tarball, it's just an abbreviated way of naming the extension.

BZ2
This extension would indicate a BZipped archive or "block-sorting file compressor". bzipping offers *extremely* high levels of compression, resulting in very nice space savings. It's not commonly used outside of the Unix environment, but, occasionally you'll run across one that's been posted by a Linux/Unix user, - or by candler because he`s a sadist. The bzip2 and libbzip2 official home page
Or, for simple extraction on Windows-based machines, WinTarBall

SIT
Stuffit Expander for Windows Mac and Linux

ARJ/JAR
Winarj for PC users or DeARJ for MAC users
Yet another type of compression. ARJ is a file archiver that compresses files into a disk space saving archive. It is fast, reliable, and has a rich set of features which include Windows 95 long filename support, file version management, data damage protection, ANSI escape sequence display handler, configurable command options, multiple volume archives (archives that span diskettes) and much more.

DeArj is the fastest ARJ decompressor on the Mac. It is also the only one with a Mac interface.

PowerArchiver extracts almost all archive filetypes with built-in compression for:
ZIP (including Quake III PK3, JAR - JavaARchiver, OWK and REP files), CAB, LHA (LZH), TAR, TAR.GZ, TAR.BZ2 RAR and BH (BlakHole), built-in decompression for ZIP, CAB, LHA, RAR, ACE, ARJ, TAR, GZIP, BZIP2, ARC, ZOO and BH. Just go and get it already.