I had the same problem, but I seem to have done a few things to have resolved it....for now.
If I am running antivirus in the background (it is not scanning drives, just lying in wait), I disable it. I also cntrl alt delete, enter the task manager and end processes for things I don't need (ipod services, mediaplayer sharing, diskeeper etc). I went to this webpage and disabled features (ended services) that were recommended to free up some resources http://www.blackviper.com/Windows_7/servicecfg.htm.
I also made sure I had a small paging file (2gbs). It seems you have plenty of RAM (12gbs??) and that seems like overkill to me...I wonder if one or a few of your memory sticks are "inop". Perhaps there is memory testing software that you can run.
I'd be interested in hearing what the rest of the community has to say.
Win7 64 bit
4gb ddr2 800 speed memory
nvidia gx285 video card
E8400dual core processor 3.0 ghz overclocked to 3.6
