Vista didn't break that much/anything for me so I cannot really comment on this, but 7 has generally been received much better as far as I'm aware.
Why wouldn't you?
Not sure how well it runs older games as I don't usually play them anymore, but the higher versions (professional and ultimate I think) come with an XP mode that might help in that regard, haven't tried that though, you may want to look around on the web if that's a big concern for you.
Bookmarks