Vista, Windows 7, XP, Windows NT, etc., all proceed from the same code base, which is that of the original Windows NT (a very well-written operating system). So it's essentially the same OS under the hood, and has been ever since NT came out. The older Windows 9x and its ilk were a completely different code base that evolved in haphazard fashion from Windows 3.x, and they were garbage.
I haven't seen any particular advantage to Windows 7, and it's a lot slower than XP. I wish I had a hundred XP installation CDs, since it now seems to be impossible to find in stores. As every system administrator knows, never, ever "upgrade" something that isn't broken.