As previously said, "However, if you think you might upgrade to Win XP, then make the OS partition a good bit larger, perhaps 7 - 10 Gigs. Win XP has features such as System Restore and Hibernation which need a significant amount to space." My guess is 7 Gig would be plenty, probably more than enough. It's hard to say without knowing the details of how many programs you want to install. Again, programs can still be installed on D if necessary. And, if you usually store your files in Win XP's My Documents folder, which, by default, is on the OS partition, you can and should move it to D.