I'll say it: Vista is an underrated OS; I'd take Vista over XP any day of the week. A $500 laptop can run Vista without too many problems now--that wasn't the case when it first came out, which is what killed the OS. If you value gaming and security, however, Vista over XP is a no-brainer; what is more, there are some really nice Vista features that most people are completely unaware of, such as speech recognition.
With that being said--since I do understand technology--I would much prefer building, or even buying an AMD/ATI desktop with Linux for half the price of a Dell. It's ironic that Microsoft built its empire on senseless marketing now that it is being destroyed by it.