1) Most important thing before upgrading a BX board is to make sure that there is BIOS support for fcpga. If there isn't, then this chip will run cacheless, i.e. very damn slow. Flash your bios before you install this chip.
2) You need a slocket. If your motherboard can't do the default voltage, 1.7V(1.6V?), you are going to need a slocket with voltage. If you don't, then your motherboard might not boot cause it won't recognize the chip voltage
Running these at 1.8V is not a problem. I've run them at 2.1V before, people will cringe when they here that number though... I'd try to stay as close to 1.8V as possible, but we are only talking about a $40 chip here, you won't cry if it dies in a year. If your chip runs hot, get better cooling, if your chip won't overclock as high, get better cooling.
Overclocking? These should hit 850. But, as always, your results may varry. Between my friends and I, we've had three that all did 850 at 1.8V. This is definitely a better bet than the faster celeron ii's.
EDIT Forgot to say that you need a slocket that supports FCPGA. PPGA celerons have different pin-outs. Usually, FCPGA slockets have a jumper that allows you to choose either FCPGA or PPGA.