At first I thought my overheating problem was with my 6800GT, so I bought and installed a NV Silencer and that keeps the GPU temp at a max of 70c, which is real nice. The problem is, I still overheat while playing certain games.

When I overheat, my speakers make a loud buzzing sound and I see a kind of checkerboard pattern on my monitor. I don't know where to start looking, any suggestions?

Specs:
BFG Geforce 6800GT
AMD Athlon 64 3200+ socket 939 CPU
Soltek SL-K8TPRO-939 mobo
XP Home SP2
1 gig PQI Turbo PC-3200 DDR RAM
Western Digital HDD
Antec 420w power supply

Check your CPU temperatures, that might be it too.

Do you use the stock cpu heatsink/fan?

what do you mean "you still overheat"??

you have solved your GPU heat issue, yet you say you are still overheating generally speaking, the mobo would shut the system down if you were "overheating"

No, I use a Thermaltake Silent Boost.

The system doesn't shut down, it just goes to a really strange, almost checkerboard screen. The checkerboard has the colors of what was usually on the screen at the time, just really small and a bunch of them. It's a really strange problem. =\

I read a while ago about this problem (sorry cant remember where) and it turned out to be a chipset problem....you could do a google and see what comes up?