To avoid reposting information already freely available, here’s a link to the best guide of BT on the web.

I personally use Azureus as my client but I’d recommend BitComet to any new users. As for Trackers my favourites are IsoHunt and TorrentReactor. Plus I have my own for experimentation. Also if you worried about investigators monitoring your machine use PeerGuardian

And remember the two motos for BT:

  1. Give and Ye Shall Receive
  2. Share not steal