Ugh... Maybe I should write a FAQ about this.
Officially for 100% support, you need 1.12 and the most recent BIOS.
However, if you update your BIOS and your board is 1.02 or later it will still most likely work. Kroffty is correct. With the oldest boards you will need to run at 1.8 V, which is OK for a Celemine, especially since Celemines are showing up in the stores with a default voltage of 1.7 V anyway. With newer pre-1.12 boards, you can get lower voltages, but sometimes you can't support voltages like 1.65 V which some of the Celemines want. However, with these same chips and boards, 1.7 V will work fine, so that's why you MUST get an FC-PGA Celemine with voltage-jumpered slocket with the Asus P2B. On an older system, a Slot 1 Celemine simply will not work because the voltage setting is locked and your board might not support that voltage.
See my sig. It is a revision 1.10, and it works at stock voltage (1.5 V) when running 533A. I have it currently set to 1.8 V.
So I recommend:
1) Buy a Celeron 566
2) Buy an MSI MS-6905 Master slocket
3) Buy a good heatsink/fan
4) Buy good $2 heatsink grease
5) Update your BIOS to 1012
6) Set the voltage to 1.8 V (to start with)
7) Keep the FSB at 66 (not 100 to start with)
8) Install everything
9) Boot
Everything should work fine if you have at least P2B rev. 1.02. Once everything is confirmed to be working, then you can play around with all the settings and go for 100 MHz... or higher.
By the way, you'll be happy to know that all 566 chips are either cB0 or cC0. Should overclock VERY well. Mine does 920 100% stable, and 960 stable for a day.