Configure Modem for Bittorrent downloads
Solution 1:
You need to configure port forwarding , depending on the modem/ router the steps will vary. Find our what port your client is listening on then visit http://portforward.com/ for steps to configure the modem / router
Solution 2:
If you talking about dial up modems then, there is no special configuration that will help you achieve greater speeds. Your p2p speed will depend on overall connection speed of modem 40kbps, 52.6kbps, 128kbps and so on. Also speed will depend on peers who are seeding files to you.