Running x64 version now I've figured out how to disable the requirement of signed drivers and got my Audigy 4 Pro working
So, for anyone having trouble with x64 Vista drivers:
1. Hit Windows Key + R to bring up the Run command window.
2. Type cmd and hit Enter.
3. At the Command Prompt, type "bcdedit /set nointegritychecks ON" (without quotes).
NOTE: If you using an Audigy sound card, just download the Vista Beta driver dated 10th November 2005, unpack the .exe to the desktop with WinRAR and point Update Driver Software at C:\Users\
Yourname\Desktop\SBAX_PCDVTBETA_US_2_08_0002\Drivers