Why all the hating on XP 64? I ran it for years with absolutely no trouble. If you took a random person and installed XP 64 instead of 32 on their system I doubt they would care or notice a difference.
As for the guy asking about reverting to XP I don't see the point at the moment unless you already own an extra copy. With the specs on your laptop I'd say just stick with Vista, it has more to offer then XP in future terms.
However you mentioned you have an HP so I'm just going to guess that you will want to format and reinstall vista as HP has a habit of slapping all this extra crap on your system you don't need that makes it a lot slower.
If you plan on upping to Win7 then just stay with Vista right now, the two are very closely related but with key differences. Don't tell anyone but I'm trying out the leaked build 7000 of 7 and I must say I like it a lot compared to XP and Vista.