Sorry to hear you guys are having problems with this awesome game .. I didn't have any problems with my install and haven't had any issues playing it either.
I have win7 x64 home premium, and 2 ati radeon 5770's handling the graphics. I think I might have gotten one message saying that it wasn't "supported" during the installation, but thats all.
I'm not sure if Sacred 2 has the same copy-protection on it as another Asceron game, Darkstar One. Darkstar One would not run on my machine, spitting out a message about a missing/out of date dll. The problem was actually with the Tages copy protection software running on any 64-bit Windows. Tages has issued an update for their software, and it fixed my DS One install.
I had Darkstar One and the Tages update installed on my win7 x64 machine before I installed Sacred 2. Maybe installing the updated Tages will sort out the problems you are having with Sacred 2.
You can download the tages protection for x64 from the Tages website. I've listed the link below as a number of search results actually pointed to Ascerons website, but they have dissolved and their website is gone.
I hope it helps .. its the only thing I could think of as to why I didn't have any problems while you guys do.
Direct Link
http://www.tagesprotection.com/5.5/TagesSetup_x64.exe