I think somebody already asked, but what are you expecting from installing Vista on that laptop that you can't get with XP? Most of the good features Vista introduced can only be used on a fast machine, and if you consider Vista to be more secure (I think there were less reported exploits compared to XP in the last few months, although I guess they were also a problem if you turned UAC off in Vista) there are some ways to make XP at least as secure as a default Vista install.
For anybody interested in how to do this, check out
hype-free: Windows XP High-Security Configuration . This "guide" makes your XP configuration so unique that very few exploits will still work on your computer, because (as far as I understood the guide) they usually don't copy the trojans to C:\Programs to be runable in this configuration