I have the excact same problem. I tried shutting down everything but the system-processes and the game-related but it did not help. I didn't have this problem on XP or Vista, it workes just fine in those. It's like I can play like 1min then I start getting these ping raises. Then it stops for 1 min and comes back.
It's very annoying especially in Counter-Strike where you can't let your guard down for a second. I get the same problem too when my friends are playing on my local server through internet. I mean that they get big ping there.
It would be really nice if someone would come up with a conclusion to this, so I don't have to reinstall Xp again.
I am currently using Windows 7 Ultimate 64bit RTM
Nvidia GeForce 8600 gt GPU
Intel Celeron 420 1.60GHz CPU