a guy in my windows xp class has a macbook pro and he has vmware i forget macs version of it but anyways he has windows vista running on his macbook. he can switch on the fly between windows vista and the mac OS running at the same time.
if your going to get a PC laptop... get one that has driver support for Windows XP and put that on it.
vista runs slow on laptops if they have 2GB of ram. if you get one with 3 or 4 GB of ram, a fast CPU, and good graphics card then vista will run ok...