I've had this problem at stock clocks / voltage in Dead Space. However it seems to happen with unstable overclocks more than anything. Adding voltage ( afterburner ) usually fixed the issue. However the fact that this happens at stock clocks and voltage under some circumstances isn't cool. I will have to test if I can manage to get Dead Space to behave by uping the voltage past 1.162 at stock clocks. It is really sad if the vendors / ATI didn't ship their hardware with adequete voltage settings in the BIOS though...

I'll mention this happens for me with all drivers which support the HD5xxx series and on both Vista and Win7 x64 ( haven't tried x86 versions and I don't honestly care )