I’ve been running CS2 on Windows 64 pro for about 6-8 months I think, probably more but I can’t remember when I built this box. There are no issues at all with it, and the speed difference is marked.
In terms of RAM, you won’t get the full bang you would with a true 64 bit program, but it’s still well worth having the extra. I have 12GB in my current machine. With Xp64 CS2 will still only directly access 3GB, but the next 2 or 3GB (forget which) are available for plug-ins to use directly, which speeds up a lot of functionality. There is some info on this available on Adobe’s site, but I don’t have the link handy.
I’ve recently added some RAMdisk software from SuperSpeed and assigned the last 6GB of my RAM to that, and set that as my primary scratch disk. That also made a notable difference (about 20% on average). That software was only about $50 and so far has seemed well worth it.
This machine has a number of upgrades over my non-64 bit system I was using before, but it’s about 400% faster overall (yep, that much faster), and I’ve found Pshop to be extremely stable even with very large files (in excess of 2.5 GB).