I\'m not a pro but The p3 runs at 100 or 133 fsb has an l2 cache of 512 or 256 ,and the Celeron is a 66 fsb and has 128 l2 cache and the level 2 cache makes it faster (or the memory specifications -latencies - ) .
try disabling your l2 cache in the bios and you will experience the differnce .
The celeron is cheaper.