you need to forward some ports in your router/modem (if the modem doubles as a router like mine) or put the modem in bridge mode. Google "bittorrent port forwarding"
Thanks Neil is that the only thing i can do to get a faster speed? i used to download at 50 kb's now all the torrents are downloading from 15 to 0.
Which router are you using? As I know that apparently the WRT54G(S) has problems with P2P and your described problem is a symptom.
I've still to get download speeds over 250. My average is about 100. I can't figure out what the fuck is slowing it down. <_<