Well in theory, you could put a much faster cpu in the board, however, you may not get it any faster than 700 MHz. Another consideration is the memory speed. If youve got PC66, youll have to get new memory, or there will most likely be problems. Also, that board probably wont support coppermine P3s or Celerons either. Your friend may want to consider a new board and processor. Yes, you can buy a PIII faster than 700 MHz, but there is no guarantee that the board will let you run it at its rated clock speed.
700MHz is fine, but if your gonna upgrade the procssor, might as well get a new board to go with it.

He's got PC100 memory and is running it @ 100 now (Celeron 366 @ 5.5 x 100 = 550). I don't think the board will have problems with coppermines or C2s. Isn't the P3 700 (that is supported according to Abit's site)a coppermine? (The one I had was.) Before I tell him one way or the other, I'd love to hear from somebody that is running this board with a > 700 CPU or at least somebody that tried and failed. I just want to give him the right info so he can make his choice knowing all the options.
 
Thanks.

Right now I have that mobo on one of my systems, the abit bx6r2 and I am running a p3 800e mhz processor on it, with the current BIOS, QR, I think, you can set the multiplier up to 9x, so you could put up to a 900mhz slot 1 chip with that mobo, you have to set some things up in the bios, like no error-check or something like that as well, I have had it like this for about 3 months, and no problems at all.

I dont have that board, however, just because someone has successfully run a processor higher than what the board is specified to handle, doesnt make it necessarily a good idea to run a processor, even one thats not overclocked, on it. You may not have any problems at all, but boards have their limitations. I would avoid doing a BIOS update unless youve got a bunch of problems with your configuration, mainly because if you screw up you wont be running that system anymore without a new bios chip. Unless that board has a backup bios chip, you really shouldnt think about up[censored] it. At the speed your at, its probably a good idea to consider a new board to go with a new processor. Im not saying you'll run into any problems, but it seems a little risky to use a processor with a board that doesnt offically support it.

This topic comes up all the time on the ABIT news group. You can use any 66 or 100 MHz FSB processor mounted in the ABIT BX6-Revision 2 motherboard that will fit, even with slotket adapters.
However, ABIT quit up[censored] the BIOS at revision QR (which is what I use) so the BIOS does not recognize and automatically configure the settings for newer processors so if you use one of those you have to set up the BIOS settings manually.
The highest Celeron that the QR BIOS recognizes is 600 MHz, so when I use a 633 MHz Celeron with a MSI slotket in my BX6 Revision 2 motherboard I have to set the parameters manually.
The voltage does set automatically for Celeron 2 and Pentium III processors so it will not cause problems on initial setup.