I have the same problem I think it might be related to my graphics card, I've tried also with trials of parallels worstation and workstation extreme and in every case I can't enable 3d acceleration. Which graphics card were you using?
Afaik Parallels 4.0 doesn't have 3D acceleration. That got introduced in Parallels Desktop 5. If you're on 4, maybe it's time to upgrade. The current version is 7.
I'm sorry... I was reading the wrong forum... as far as I know, Parallels for Non-Macs doesn't do 3D acceleration. Even Parallels Desktop for Mac doesn't do 3D for any OS that's not Windows, I believe.