try running Windows Update from Vistas Device Manager :
open Devicemanger, locate the soundcard, rightclick it and choose "Update driver" - tell Vista to search automatically for the best one, it will search online first.
In most cases it is succesfull. Vista has very few soundcarddrivers per default. It is normal that they come via online update.
If this isn't succesfull you may use XPs drivers this way : if it is a setup.exe, you must extract it ( with winrar or similar extractors ) to your Harddrive. The content must show a *inf file and some *.sys files afterwards.
Repeat the step via Devicemanager like written above, but this time tell it to "search on the computer for updated driver software". You need to point that wizard then to the Folder where you have placed the extracted XP drivers. If these drivers are suitable, Vista will install them ( after showing a red warning that this may be dangerous ).