I'd like to suggest that you download PC Wizard 2008. It's free. It also has a Temperature utility that will show temperatures for several of the PC's components. When you first start this up, you need to go to the Options and set it to show the temperatures in 'real time'. Be sure to check around in there to make sure you have all of the components selected. Once you have this active, minimize this to the Task bar and you should see the data in the top right corner of the screen.
Pay close attention to CPU/Processor temperatures as well as the GPU and others.
Download from here:
CPUID
I would also check the RAM timings in BIOS to make sure the RAM is running at spec. You might even try loosening the timings a bit to see if this helps. If, for example, you're running at 5.5.5.18, up the numbers one notch to see if things work better.
Good luck!