I have a ASUS laptop and have alot of problems with latency spikes that cause dropouts when running DAW's and weird granular sounding glitches when listening to music, like 2.13 in here . Which seems to be caused by a loads of different things which is really frustrating and a pity because they have got a really good reputation.
Firstly the integrated NVIDEA card that comes with asus laptops has really bad drivers that cause this, you can get some software that seems to make it better by changing some settings you cant change manually. But also coming from sleep mode or having a system resume will mean that you recieve these large latency spikes also, and I wouldnt be suprised if windows 7 is a culprit aswell.
I think (not sure about this though) that the biggest resources hog of windows 7 vs XP is the "aero" GUI which you can turn off, I quite like the OS to be honest but I think XP is probably a good idea. I'd also be wary of asus laptops because of the problems I've been having with latency spikes which I havnt been able to find any concrete resolutions, but maybe look up on the specific model you are thinking of getting to see if anyone has talked about having specific problems, especially with latency spikes because they can be caused by loads of things, not just what I mentioned but network adaptors, usb drivers etc. I have managed to get mine running, when all the right conditions are met, pretty much without any audible latency spikes (the latency checker still shows quite a few but they dont effect audio/video), but really I'd avoid anything with those NVIDEA G100 integrated gfx cards like the plague.