This seems to be a good guide to overclocking the Athlon. Covers your FSB overclock method, as well as a hardware mod to unlock the multiplier on the processor, allowing for more stable overclocking.

I also found this guide complete with a video, though this method looks a bit more dangerous and harder to reverse if a mistake occurs.

Unfortunatly I have no personal experience to insert here with the Athlons and overclocking though.