Right, first off there's a subscription. These can range from $5 to $20 for a basic subscription but there are two things you need to take into account:
1. How much you can download
2. Wht the retention rate is.
In regards to 2, the retention rate is how old the files you can see are. These are usually 30-90 days, so you don't get much of an archive.
The service I used to use is http:/www.easynews.com . $9.98 a month for 20gb, but only 12 day retention so you do have to be on the ball with checking your groups.
As for a client, I used
http://www.shemes.com/ (Grabit). Easy to set-up and browse and has .nzb support (Where you can download a .nzb file, put it into the client and it will grab all the files as most downloads are split over 50 or so files.
PROS:
Stupidly fast
Most games/apps/movies go on newsgroups before anywhere else
CONS:
No archive of old downloads
There is no error correction, so your files will download incorrectly, and often. But there is a fix to this.
As well as downloading the RAR files, you can download PAR files. Basically, it will fix a broken download of rars automaticall for you (Only a certain amount, if the whole downloads buggered, you're screwed.). If you get this far and want to know more abot .PARs, let me know.