I'd go with an abit or a Soyo board personally, but that's mainly because I'm an over-clocker.
I don't reccomend you worry about getting a board what will theoretically support a P3 slot1 for a couple of reasons. First, by the time you are ready to upgrade again you will need a new mobo to support new features such as DDR RAM, AGP4X, ATA66/100 etc. Second, the coppermines aren't going to be produced much in slot1, and I doubt you'll see it used much in the future for consumer level chips.
What type of CPU connection is in the mobo you have? What front-side bus speeds will it support? If you are going to buy a new mobo though, get an Abit. It will overclock a Celeron with very good granular control, and has all the other bits like ATA66 controllers.
If you aren't into the over-clocking thing though, just get a fast Celery and whatever mobo your supplier wants to slap it on. Usually the price difference between a good mobo and a not-so-good one is very low though, so I usually get a good one. Your mobo is by far the most complex and succeptible piece of hardware in a computer, so it always pays to buy a quality one. IMHO
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Lephturn
The Flying Pigs
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