Ubuntu
I decided to simplify my life and not install Ubuntu. I also got a Dell which came with Win XP Media Center Edition, which sounds like a spinoff of Win XP Home, but is actually--and I discovered this the hard way--a descendent of Win XP Professional. So far I love the Dell's performance. But the SATA hard drive I added to it is noisy. It's a Samsung drive so it's mostly Samsung's fault, but the case could be better insulated against noise too.