And XP is slower than 2k.
Personally, I've seen PCs with Win2k being really slow, then upgrading them to XP (SP2) and then going a lot faster. I'm talking about old machines, 256MB of memory or not more.
Why choose XP over Vista, then? First, no useless graphic effects. Please, don't say you want 300MB of your RAM wasted for Aero, when you could use them when they are required by applications. Second: with a machine that barely supports Vista (3.5 points and down), you have a very efficient XP machine. Third: hours to copy a DVD with Vista, when you could copy it in some minutes in XP? Also, the support for audio devices is better in XP now than in Vista (and Windows 7 also). Fourth: stability and longevity. No other words needed on this point.
The first rule of intelligent tinkering is to save all the parts. -- Paul Erlich