i had a cellery 500 on a sweet asus board, but i think the 500Mhz celleron is the much older .25 micron die size, and i couldnt get mine anything over 600mhz
e.g. it worked at a FSB of 66 and 75 no probs, but just died trying 83, even with 100mhz ram and the agp multiplier turned to 2/3
i just dont think the 500's were built for overclocking.
cellys are pretty much dead now anyhow. get a duron