Vista SP1 failed to find Soundblaster Extigy USB soundcard :

 This guide works with a clean Vista Ultimate install (SP1 slipstreamed Vista DVD)!

 Recommended tool : Download & install Unlocker

 Easy part :
 1. Search your system for the old USBAUDIO.sys driver:

 2. Copy old USBAUDIO.sys, (d.02-11-2006) to usb or floppy

 Tricky part :
 3. Go to C:\Windows\System32\Drivers
    Rightclick USBAUDIO.sys (d.19-04-2008)> Unlocker > Choose Delete

 4. Copy old USBAUDIO.sys, (d.02-11-2006) from usb or floppy 

 5. Reboot Vista

 This enabled my Extigy Soundcard !