Ok without sounding like a vista fanboy, Not xp 64 bit, vista 64 bit.

XP 64 bit has REALLY bad computability issues, where as since vista is the new operating system and Microsoft don't want people buying XP, they have made vista 64 bit pretty much just as compatible as 32 bit.

Ive always hated vista, i got vista 64 bit and never went back.

You don't need to get it, only if you want 4gb of ram or more. only reason you should.

Answer:
Apart from a few Microsoft slaves who 'd state yes, the answer you need is NO. 64 bit operating systems offer no advantage yet although they might be able to catch up in the future. It's not just the Operating System you'll need special versions of software especially adapted for 64 bit and they are few and far.
Answer:
I agree 100% with Kramer. I run 64bit Vista and althou a lot of people I don't even think have 64bit Vista state it has terrible compatibilty issues I haven't had any. Can't say that about 64bit XP thou. I put 64bit XP in then yanked it because it was so bad. If you like XP stay with 32bit XP and save yourself some grief. 64bit wont be mainstream for a good 3 years or so. I run 64bit Vista in my Vista gaming rig because its over 10% faster than 32bit Vista BUT my XP gaming rig, althou its a 64bit system, runs 32bit XP.