Personally speaking I wouldnt have ever have 14-24 programs running at once; i can barely manage keeping up with 3-4 my self ( FBIDE, WinAmp and Internet, sometimes messenger )
The game in question might have updated patches for Vista now try checking the manufacturers website, as in your spec for zero hour theres no mention of it being compatable with Vista. I suspect it might act up, if its trying to use direct sound the XP way as in vista sound is dealt with completely differently.
Thats why I suggested running it in compatablity mode for XP. click the shortcut to your game, and select the appropriate os to emulate under.
I had to do a dual boot of XP and Vista, so that I could play some games in my collection that just dont run as should be.
I would make sure you have the latest drivers from nvidia or ati for you gfx card, also make sure you've got the latest directx.