Parallels screwing up system / hanging a lot.

I'm using Win-7 on some VMs. Since two weeks the situation is really bad.

1. Parallels is hanging a lot and I need to hard close it. It's just not reacting.
2. Sometimes the whole OSX system is locked up and I need to switch of my system.
3. My screen gets screwed up with artifacts. Looks like screen areas are not refreshed/redrawn and than the VMs hangs.
4. Sometimes the VMs just fall down and I see the black boot screen.

System: Mac-Pro, OSX 10.6.2, 32GB Ram, Nvidia-8800GT

Using the EN 9310 build.

I'm not sure if something in OSX, Parallels or Win-7 changed, that made it that worse. Is this a "known" problem and any idea how to fix it / when Parallels will be fixed?