Install MotherBoard Monitor to help you monitor the CPU temperature to see if it is heating problem. It can also help you to check if how fast your CPU fan is spinning (in rpm) Normally the CPU fan should spin faster than 5000 rpm. A good CPU fan is important for AMD chips (known to be hotter than Intel)
Below is the website for MotherBoard Monitor
http://mbm.livewiredev.com/
Beside fan can use software to help cool the CPU. Try CPUIdle. It is a software that will issue halt (or suspend) command to the CPU when it is waiting for other devices like keyboard, harddisk or mouse etc to respond. It is like temporary stopping the CPU and can help the CPU cool down a lot. I am using an AMD Athlon 1.3 GHz. Without CPUIdle, my CPU temp is 56 degree or higher. With CPUIdle, it is constantly below 50 degree.
Below is the website for CPUIdle
http://www.cpuidle.de