Just realized you highlighted the most important part masteff. Agreed. The removal of the security check as part of the 2.28 patch is likely the whole solution. While googling the error message I got, "Error loading x64 driver. Did you forget to reboot?", I read several mention that DRM was causing the problem. Great info!
Well I just had to give this a try and it went very well. So here's how it went for me:
My basic specs:
Windows 7 Home Premium 64 bit
Intel Core 2 Duo E8400
DDR2 8gb Ram
UAC is active the whole time
Security Essentials protection active the whole time
How I ran the installer:
Browsed the install disc and ran as admin
How I set the shortcut:
Run as Admin
Forget setting compatibility. I just turned those settings off and left the shortcut as a normal shortcut and the game still runs fine.
How I set sacred underworld's config.exe found in the install folder of Underworld:
All Graphic settings off
Sound activated on
After running the installer I tried to run the game which gave me an error. "Error loading x64 driver. Did you forget to reboot?". After some googling I finally realized that I hadn't installed the Underworld patch 2.24 to 2.28 yet. I ran the patch and as soon as it finished I was able to play Underworld. No problems that I can see. Tried running an SP game and a LAN game, both of which worked just fine.
So on my system it was a pretty smooth process.
One problem I had at the very start was that the window froze when I first tried to run the cd installer. When I ejected the dvd only then did UAC ask for permission to run the installer. A slight glitch in the UAC process...