http://www.bi-torrent.com/
http://www.torrentreactor.com

Best Client is Azureus

http://azureus.sourceforge.net/

Basically you then download the very small .torrent file from various torrent sites. It will then create was appears to be the entire file on your hard drive (Say a 700MB avi) and then it will download small chunks from all the seeds (people who have downloaded 100% of it and are only sharing) and leeches (people who are downloading it but not finished)

The main problem is you are way too late in the day really to be catching on to BitTorrent. Suprnova (the biggest free, non registration site) has been closed, as have lots more. So lots of the registration only sites are no longer accepting registration because of it. Some sites only work on referal.