Right, so the only 32-bit software that you cannot run on a 64-bit OS is kernel-level stuff. This includes drivers and CD writing software, for example.
It's rather unfortunate, actually: due to the fact that Windows has for all time allowed administrator access to be the default, some software developers have had no qualms about including kernel-mode stuff where it really shouldn't be. So unless Windows Vista has some kernel-mode emulation for Windows XP and previous, there's always the possibility that some 32-bit software just won't work.
But any software developed for Windows Vista 32-bit should work great on Windows Vista 64-bit.
It's rather unfortunate, actually: due to the fact that Windows has for all time allowed administrator access to be the default, some software developers have had no qualms about including kernel-mode stuff where it really shouldn't be. So unless Windows Vista has some kernel-mode emulation for Windows XP and previous, there's always the possibility that some 32-bit software just won't work.
But any software developed for Windows Vista 32-bit should work great on Windows Vista 64-bit.