LinuxQuestions.org - Interesting Problem with a Inspiron 9200

Ok, I've been living with this problem for the better part of a year, but have been unsuccessful in figuring out what is actually causing it.

Hardware:
Pentium M 2.2GHz processor
2GB of DDR RAM
ATi Radeon Mobility 9700 (256MB)

Software:
Slackware 12.1 with 2.6 Kernel, Fluxbox WM, and LILO boot manager

Symptoms:
When I boot my laptop from a cold state, the system performs just fine and usually continues to do so for about an hour, depending on what I am doing. But after the laptop reaches a period of runtime, the processing speed drops significantly. I use torsmo embedded into my Fluxbox WM, when I boot my laptop, it shows 2200MHz for my processor speed, but once I begin experiencing problems, my processor speed drops to 500MHz.

Solutions attempted:

- I have reinstalled the OS multiple times, even trying different distros with the same result on all.
- I have updated the BIOS.
- Changed my RAM out.
- I have reinstalled my video card drivers to a friend of mine's suggestion that the X-server wasn't recognizing my video card and using my laptop's processor to compensate.

Anyone else have any suggestions? I'm almost at the end of my rope with this laptop...if you need more information, just ask me for outputs. I'm afraid my processor has kicked the bucket, but finding a replacement is difficult.