I had a similar problem once and was able to completely resolve it.
My newly self-assembled system would crash whenever certain video-intensive applications were run, including Windows Media player. Even rapidly moving windows around on the screen would cause the machine to crash. Turning off Windows video acceleration (moving the slider all the way to the left as described by "OZ Media") was a 100% effective workaround. Stable system but crippled video.
How the problem was completely corrected
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The root of the problem was the motherboard's BIOS for its onboard peripherals. I downloaded an updated BIOS from the motherboard maker, flashed it using the provided utility program, installed the latest motherboard-based peripheral drivers from the manufacturer, and the problem went away. I was able to turn Windows video acceleration completely all the way up and the machine has been 100% rock solid for about a year now. The hardware: MSI K7N2G-ILSR motherboard with onboard GeForce 2 VGA and shared memory, AMD Athlon XP 2200 CPU, 1.5 GB PC2700 DDR RAM.
There was a timing problem that was resolved by the BIOS (software) change. This is reflected in your observation that changing the CPU and bus speeds seemed to change the behavior.
What to do
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1. Workaround: Reduce or turn off Windows video acceleration as described by "OZ Media". You should only need to reduce video accelleration to the point where the system becomes stable. Start with "off". Bump it up one step at a time and retest until the system destablizes. Then, back off one step.
2. Download and install the latest motherboard drivers and/or BIOS from the motherboard maker. Retest with full video acceleration on.
3. If you have onboard video, disable it (jumper or BIOS setting) and install an AGP or PCI hardware video card. Retest with full video acceleration on.
4. If the problem persists and you want more video acceleration than you are able to achieve without destablizing your system, replace the motherboard with a different make/model. Video acceleration is important for the best visual experience on Windows XP.
If you solve or improve on your problem, let us know what you did and how well it worked. Good luck!
-----Steve Jackson
CEO
Software Corporation (Softcorp)
http://www.softcorp.us