That would suggest some sort of heating issue to me or possible power supply problem. Again, check for dust and get the powers supply checked. It should bluescreen immediately if there's a driver issue, and the problem should be repeatable, instantly (you shouldn't have to create 3 backups just to reproduce the bluescreen).
Run system stability tests (everest, orthos, Prime95, 3dMark06 on repeat for about two hours)
I'd also run memtest and check your ram (if you have two sticks, try runnning with one stick--and then the other).
I'll cover my eyes and pretend I didn't read that.
I prefer using Arctic Cooling MX-2. Again, I find that Zalman cpu cooler just cylces hot air inside the case. I've overclocked a lower end intel quad 45nm core to 3.6ghz on air. CPU Idle temps were around 28C. Max gets into the high 40s, but that's still fine. It's Prime stable over 24 hours. I tested the zalman hsf and my case temps rose by 10 C over the Thermalright Ultra 120 Extreme with a Noctura fan and also with an OCZ Vendetta 2 (I don't like how the OCZ Vendetta 2 ends up slightly bending the motherboard).
I find myself unable to reproduce your issue.