Newer processors come with a cooling mechanimism that dynamically adjust voltage and frequency depending on the demands of the processor. For Intel it's called Speedstep and for AMD it callded Cool and Quiet. If the computer is idle then the processor throttles down to help lower heat dissipation and electricity.
To enable this function you must have it enabled in the bios, drivers installed for Windows XP and have power scheme that allows for it like "Portable/Laptop" or "MInimal Power Management". You can download the drivers at the AMD website. Also download AMD Power Monitor Version 1.2.3 so you can watch Cool and Quiet in action.
Now in my experience when CnQ seemed to be working fine, when I watched a movie CnQ becomes disabled and stays disabled. It doesn't matter what program I used either Windows Media Player or VLC. I looked some forums and found that others are having the same problem though they seem to not have any solution. I contacted gcc.asia@amd.com which I found in their contact page. And they said to update my bios and change the ATI Hotkey Poller service from automatic to manual. So I did that and it worked. The thing I noticed about flashing the bios is that the date of computer changes to the day the bios was released and the energy star logo under Monitor Power is gone. You can change ATI Hotkey Poller by right clicking My Computer, selecting Manage and going to Services and Application. Watching videos does not disable Cool and Quiet anymore.