Oh, I'll probably upgrade to Windows 7. I've used it a couple times at a friend's house. It seems pretty neat. Better than Vista at least (my laptop that I gave to my mom, who then gave to my bro, who then threw it in a closet...used Vista). It just depends on what the computer shop down the street has, though they usually have some good variety.
As for Building a PC, I have to upgrade everything, my comp's so out of date, and then I don't really see the point, I may as well just get a totally new machine.