Pretty much all Windows 32-bit programs should run without error on a 64-bit version of Windows because there is a whole dedicated subsystem that emulates the 32-bit Windows system.

An important point that Redrobes touched on is that you get MORE memory running a 32-bit Windows program on 64-bit Windows. http://kb2.adobe.com/cps/404/kb404901.html shows that 32-bit PS can use a maximum of 1.7GB of memory on 32-bit Windows and 3.2GB on 64-bit Windows.

My recommendation is at least 8GB of RAM and the 64-bit version of Windows 7. The 32-bit PS version should run a bit smoother with large files than under a 32-bit version of Windows with that sort of configuration.

Photoshop filters are programs (DLLs, technically, but the principle is the same). According to the Adobe document above, the 32-bit filters won't run under 64-bit PS version. This fact isn't surprising because Windows can't load 32-bit DLLs into a 64-bit program; the instruction sets are different.