I've had similar problems, in fact just this weekend. Here is what I did; I downloaded the latest drivers, dated October 22, 2007, I uninstalled my old ATI drivers and software and rebooted. Then I installed the newest software and driver and so far it seems to have worked.
I have two monitors and overall it seems that Vista doesn't like ATI video cards. I have a 512mb PCIe ATI X700 video card and because of it my Windows Experience Index is only at a 4.2 and is only because of my video card. I realize mine isn't top of the line but still.
Anyway try uninstalling your video drivers and software then reinstalling with the very latest. You can also try uninstalling Dreamscene and reinstalling it. (Control Panel, Programs and Features, View Installed Updates then Dreamscene then click Uninstall) then reboot, then run Windows updates again to reinstalling. Good luck!
Cheers
Rob
The answer is always "PEBKAC!