I would suggest the PIII 1000EB, which has recently come down in price to just over $100. The Celeron 1.2GHz only works on Slot 1 boards with the special, more expensive, Powerleap iP3/T adapter. And Powerleap says it won't work on your board.
I read in another forum that the P2B series won't support any mulitplier of 11x or higher, due to a flaw in the BIOS. Which leaves you to the PIII 1000EB as the fastest CPU you can use.
Now there are several things you need to check before you can use ANY coppermine CPU on a standard slotket with your system. First is that you have a new enough board to supply the proper lower voltage of the CPU. The only workaround for a system that does not support the proper voltage is to increase the detected voltage of the CPU and live with the higher voltage. For no I'll assume your board is a later revision that supports Coppermine voltages.
Now you need to have a recent BIOS revision.
And to run a 133MHz FSB processor like the PIIII 1000EB, you'll need PC133 SDRAM, a decent video card, and the FS3 jumper on your board. If you choose to run the Celeron 1000 instead, you can bypass these last requirements at the expense of about a 30% performance decrease.
What's the frequency, Kenneth?