on your laptop, I might guess that you won't have a whole signshop worth of obscure programs & device drivers that need to run on it...
I bought a Vista 64 bit upgrade just yesterday, on purpose, without a gun to my head... although I did call Casey (Signburst) first... but I went for it, and have no remaining fears about it serving me well.
As for your "downgrade" idea, running that laptop on XP... be forewarned, it is sometimes a very difficult process. More recently (last 2 years) a lot of Vista machines were built with this possibility in mind... but when Vista was newer, & M$ had hopes of more confidence in the marketplace, they assumed XP would fade away & made machines with no compatible drivers... Techman will tell you there is a way to get drivers for almost any component... but there is a way to scale Mt. Everest too... for me, after 6 solid hours of struggle, the XP OS I loaded on my Vista laptop was taken off again, since sound card, usb ports, CD drives & assorted other functionality was lost, with no luck & no optimism coming from HP tech support. I'm sure the right guy might have had better luck... but I'm not that guy, so I accepted my Vista fate & found it was nothing to fear after all... in my case.