Intro to newsgroups/usenet:
http://www.slyck.com/ng.php
Rather than take the easy route I shall attempt to explain, consider the following a (probably badly worded) crash course. Some say usenet is hard to use but if you do it right then you are laughing (my setup for me ranks easier and so much quicker than any limewire/bearshare/torrent nonsense).
The premise
Simply put newsgroups aka Usenet is a network of servers that you can access. To do so you either have to pay a provider (typically the best option) or your ISP may provide them. You will also need a newsreader.
They run sort of like a forum in that people post stuff on them and have multiple sections to describe their contents (alt.bin.monkeypictures should contain pictures of monkeys, for reference a.b. as well as alt.bin. is shorthand for alt.binaries), these messages can be text based messages or encoded files (usenet only accepts plain ASCII and few other characters so files can not be left as is, the most popular methods being UUEncode, yenc or base64).
Searching usenet
To see what is available or download something you can do one of three things:
Download headers:
These are all the posts in a group (think of groups like subforums) and you download the lot (or to a given age). From here you can pick and choose what you want. Takes a bit of space and can be a bit hard to search but it is all good.
NZB files:
You can download these from many places and they are a bit like torrent files in that they contain the location of the files you want and some data about them.
A searcher:
schemes is a pay site and binsearch.info is a free one (it generates nzb files)
Files:
Typically they are spread across multiple posts if they are big, convention has it that multiple rar files work (normally called either XXX.part1.rar, XXX.part2.rar or xxx.r01, xxx.r02 ending with xxx.rar) here so a rar reader like winrar or 7zip is necessary.
PAR files.
Quickpar
http://www.quickpar.org.uk/Download-0.9.1.0.htm
Like we use CRC32 and such to verify roms these files help verify and fix things. If it a rom/iso I suggest using a conventional manager first, if it is a multirom archive then try and extract and it will tell you if it is corrupt.
There will be a small PAR file and a larger PAR2 file most of the time, the PAR2 is the one you want for corrupt data should you have it.
Usenet providers:
3 things you want to be concerned with
retention:
This is how long the provider stores posts, you want above 60 days (most ISPs will struggle to hit 30).
completion: 99% or better. How many posts of all the ones available.
Usage limit. Anywhere from a gig to unlimited. Once you start you will not stop until you run out of space though.
Less important but still nice.
Number of threads at a time: how many posts you can download at once. 10 is nice but 20 is nicer.
Speed, for me this is limited by my connection (yes downloads happen at full speed all the time). Only a few providers limit speed severely.
The reader:
Make sure it supports the three main encoding mechanisms:
UUEncode, yenc or base64
Posting is another thing (which grabit does not do well), depending on who you speak to yenc is a good thing.
Grabit is my reader of choice although there are numerous others.
http://www.shemes.com/
newsleecher:
http://www.newsleecher.com/
sylpheed:
http://sylpheed.sraoss.jp/en/features.html
More readers:
http://www.newsreaders.com/
There are a bunch of threads detailing it all around here as well, Grabit, giganews and binsearch.info (in conjunction with headers) work well for me.
