How many DIMM slots do you have? Try switching your RAM sticks from one to the other.

It probably is your RAM, though. I'm having weird problems with memory usage lately as well. Sometimes while playing CSS or MAME, the program crashes and I get 100% CPU usage. All the memory tests I've run have come up clean, so until this starts effecting my normal computer usage, I'll continue using the RAM.

Oh, and one case fan? I have three blowing out, one blowing in and two inside blowing hot air off my CPU and GPU.