If you can't upgrade the bios on the mainboard to a new version that supports a higher clock, it simply won´t boot with a 700MHz CPU!
O my someone with a LX chipset. Is that the economical version of the BX chipset?
Best bet is to pick up a cheap duron mobo combo that will give you a good upgrade path for real cheap (less than $100). allow you to start with a 700mhz and go up to the latest and greatest(just comming out with the thoroughbred core that will use same socket)
Due to Intels platform hopping the only Intel platform with any upgrade path whatsoever is the new Celeron(P4) chips that use the same socket(put you back lots more $$$$). Older celeron boards don't accept any version of the p4's.
Intel:<i>"Thoroughbread just a die shrink - will only help with frequency, not preformance."</i>