If you want to game, your ONLY choice is windows, and you might as well get win7. I have it and it is MUCH better than XP. The UI is much nicer, the programs and applications that come with it are better, it is easier to use... good stuff.
I am dual booting Windows 7 and Ubuntu 10.04, and I absolutely love my Ubuntu installation (IMO linux > win), but installing games on it is extremely difficult... Linux can be frustrating in general to use. If you want a simple, hassle-free OS, get Windows 7.
+1 for Open Office, I love it, paying for MS word is a joke...