Not sure if you guys bothered to notice, but have you looked at the load that mining puts on the gpu?? It doesn't surprise me if it crashes when you're mining and trying to play a graphics intensive game at the same time.
It's not about load. The problem is drivers and 6xxx cards. I have two 6970 on two PCs that make PC freeze when miner is running and any video is started. And I have 3 5870 cards on another two PCs which run perfectly fine even with hardware acceleration enabled. I'm absolutely sure it is related to compatibility between 6xxx cards and drivers. Whatever load there is, it should not cause computer to hang.