Dell DOES NOT support Vista or Windows 7 for this model - just XP and DOS. You are in "uncharted territory" and basically on your own to try and find something that will work. In most cases the Retail SoundBlaster Audigy 2ZS drivers will work on the custom Dell model card. Most of the SoundBlaster's need Windows 7 specific drivers even though Windows 7 is basically Vista "improved". Check www.creative.com
for a Win 7 driver for the this card.
If you can't find workable drivers for the SoundBlaster you will probably have to install a new Win 7 compatible PCI sound card. However, whatever you install, you will most likely lose the front panel headphone and mic connections as the connector on the Dell version is proprietary.
I do a lot of hardware support on the Dell forum and don't recall anyone posting about attempting to install Win 7 on this model.