Vista On A MacBook vs XP
I have been using Vista Business on a MacBook 13" 1.83GHz for three weeks. It was very slow with 512MB of RAM. I upgraded to 2GB and it runs much better. Vista was very difficult before the latest boot camp drivers (1.2) It is still not perfect, but it does work better. I have issues of waking up from sleeping and loosing USB and wireless networking. If I had to choose I like Vista better because it looks more like the Mac OS.
At the school I work, we have been running boot camp with XP on 48 machines. It has been working well since the beginning in early June. I have had a few Winodws installs go bad, but other than that it works well. The only issue I have had, and this could be my own misunderstanding, is keyboard layout and right clicking. In Windows, it is much easier to use a two button mouse and a Windows keyboard.
My overall opinion would be XP is very stable, but Vista looks better. The only down side for Vista is the RAM requirement and the current issues, but I am sure the issues will be fixed soon.