How are you tring to install the X-Fi Drivers?
With the CD that came with it for Vista?
I would recoomend going to Creatives official Site, and download:
Console launcher
X-Fi Driver
Alchemy (if needed)
Any other software you need.
These will all run and install under 7 x64 without issue.
If you want use of the Volume Panel, and THX console, you need to install these ONLY from the Vista disc.
Do this first if you want these.
Do not let it Auto run, and browse the disk for the setup.exe.
right click and choose to run compatability mode Vista SP2.
Now run the installer, choose custom install, and ONLY install THX console & Volume panel.
then instal the Console launcher, and the XiFi Driver you downloaded earlier in that order.