all 32bit apps work xp64 i'm pretty sure, i don't think i've ever had any problems, all the games i had worked, photoshop, zbrush, mudbox, maya, anti virus etc all worked. i built both my home systems just because its really fun and a tiny bit cheaper, installed xp 64 on my own and tweaked it on my own reading from a tone of sites, and i've never had any problems. actually only problem i ever had was my 5 year old digi camera wasn't recognised but i just bought a £5 memory card reader.
i like a few things about vista, and like i said use it for gaming, but i just like xp64 a whole lot more and think it perfroms better, theres probably alot of people on here that use vista 64 and reckon its great, but i go from what industry is using, and microsoft have already shown what they think of vista by planning to release there next OS, windows 7, in early 2010 which really is that far away. i'm hoping i can pretty my bypass vista for workstation unless theres some amazing service pack that comes, xp64 wasn't that great on release and there were a tone of 64bit driver issues but sp2 release is great ,no driver issues and if you got a pc from the last few years it will work super!
i think people are too afraid of 64 bit computing, the sooner everyone switches over, the sooner it will get better and better, and then we can start thinking about 128 bit systems!