I've used SoundStorm (nForce2 chipset), SB Audigy and HDA Digital X-Mystique7.1 Gold soundcards under 32-bit Windows 2003 Server for quite a while now. (not all at the same time obviously)
Win2003 Server SP1 matches the same features as XPSP2. You might want to run dxdiag.exe to make sure you have full sound acceleration enabled, but I do not recall issues other than that. (for games and workstation type apps you'll also want to enable full graphics acceleration, but I assume you knew that already)
Direct-X 9 is of course included. (the DX9 updater on the Battlefield2 DVD will even update 64-bit Win2003!)
I'm surprised to learn that half your apps won't run under 64-bit Windows. *shrug* Remember that processes are limited to 2GB memory under 32-bit Windows, whereas 64-bit Windows can give 32-bit processes a 4GB virtual address space. So if memory is your thing, you are probably better off with 64-bit Windows. (worst case: Install each OS on seperate drives and dual boot... That way you have an easy fallback -- personally I even share the same user profile between the 64-bit and 32-bit version of Win2003)
HTH.