Problem with fileshare programs

[Sultan]

In just the last week I've started having the strangest problem with p2p fileshare programs. Whenever I run a p2p program, it totally kills my entire internet connection. The program can't get any connections itself (I've tried 3 bitorrent clients and emule) and nothing else works either, ftp, web, or even my email or a simple ping. But as soon as I turn off the offending p2p program, everything is fine again. DC++ does not cause this problem. I'm using XP SP1. Been a little nervous about upgrading to SP2 but could do that if anyone thinks it might help fix it. Anyone have any suggestions on what could cause such an odd problem with all my P2P programs?