HOW TO: Optimize Your Bittorrent Download Speed
Bittorrent can be fun, as long as you get decent speeds. Not satisfied with your current speeds? 
These suggestions might help to optimize your download pleasure.
If you’re on XP sp2, your TCP connections are limited to a maximum of 10. This might hurt your downloading speed because it wont let you connect to as much peers as you want. It is supposed to slow down viruses because their spreading strategy is to connect to a high amount of ip numbers, but it could cripple your torrent downloads. Optimize Your Bittorrent Download Speed at Torrentfreak