I see other people in several threads have had this problem so I thought I would mention my experience with my (new, fine) open GL-capable NVIDIA card that does open GL for me in P7.
When I switched to Carrara it worked fine until I changed the Carrara default preview render from "software" to "open GL" . (seemed like the thing to do!)
 Black Room! Slow! Confusion, stumbling around in the dark!
I switched back to "software" and all was smooth again.
If you futz with the NVIDIA card settings in the windows XP control room, it also sets the carrara preference to "open-GL". Whoa!