What is Asus P2B MBoard upgradeable to?

I have an Asus P2B HOT-541 mother board with a Celron 300 Mhz cpu chip. I would like to upgrade the chip, not overclock it. What can I upgrade to (various speeds, models, etc.) and what is involved besides replacing the chip. Host bus clock/cpu core clock ratio from 1 : 1 .5 to 1 : 3. AT bus clock 6.67 to 8.25 Mhz. Please, points for answers, not redirection to websites.