PS: I have to disagree with Spinflight about disabling VM - particularly if you have less than 1GB of memory.
No problems there Mac, I've read countless threads by serious dudes who will generally disagree completely on VM issues.
Windows uses half of your memory for windows itself, however this total includes the Virtual Memory. Hence if you use the recommended setting of 1.5 times physical memory and you have 1gig of memory then Windows takes 1.25 gig to load itself into, which is all Virtual. This worked wonders to help low memory users run Windows when physical memory was expensive (figure 16 and 32meg systems running earlier versions, 2K only 'needs' 128meg) but looks to be wasteful when you have plenty of RAM.
The theory behind VM sounds wonderful as page faults are meant to be very rare, however not in my experience (I expect due to lazy programming though I'm not fluent in C++). Basically when you see your computer thrashing its due to page faults with the OS swapping files in physical RAM for those on the VM. It's meant to be a 1 in a million occurence due to the statistics behind code access....
If you use games or very large applications then definately keep VM enabled, though if you only use websurfing, office etc then you can probably live without VM even if your running 256 or 512meg systems.
Personally I use XP with VM disabled (havn't yet had a problem and the performace has certainly improved) and 2000 with a smallish page file like Mac's.
One tip which most people agree on is to use a seperate partition at the beginning of another drive for your swap file, this frees up the second IDE channel for your VM hence speeding up the IO (i.e. the OS can access VM whilst still using your C: drive to run the app).
Even better is to use a RAID system seeing as though are so many cheap small HDs available.