I'm having similar problems. I'm trying to play Diablo II and all of my drivers
are up to date. It should be running perfectly. I read somewhere, but now can't find the site, where people reported the same issue in Vista.
Basically it came down to it being a problem with Windows automatically checking for wireless networks every 60 seconds. Does your lag follow this pattern?
If so we're having the same problem.
I would also like to fix this problem, since like you said, Windows 7 is superior to XP and Vista, of course.
It seems to me we must find a way to disable Windows from automatically checking for wireless networks.