It's all about voltages. A CPU FSB of 400 usually requires 1.63v on the NB. 450 FSB 1.67-1.70v. 475FSB 1.70v+

Also the CPU needs 1.325 for 450FSB. and with VDroop 1.355v.

If your your BIOS doesn't have the full barrage of Voltage adjustments you are screwed, more than likely.

You need to tweak NB to 1.75v, CPU Pll to 1.75v, FSB vtt to 1.50v, CPU to 1.45v, sb to 1.175v, etc.