Playing games=1/10 download speed

I have a dual monitor setup and I try to keep my downloads running on one of my monitors (with bit torrent or just regular downloads) while I try to play a game, even an offline game, and my download speed will immediately drop to say 20 or 30kbps where it was downloading at least 200kbps not a second before I was running the game. If I minimize the game I can watch the download speed dramatically return to normal 200kbps, putting the game back on top of course drops it back down. What the heck is going on? How do I fix this? I've already tried reformatting. Thanks in advance for your help.

I'm running vistax86 business on service pack 1
intel duo 2.4ghz dual core
nvidia 7900gs
2gb ram