BlargOC have posted a guide to overclocking the Tualatin PIII and Celeron. Heres a snip:
"Intel have really made quite a come back recently in the overclocking scene. Their Pentium 4 Northwood cpus are excellent overclockers, and the 1.6A and 1.8A versions are excellent value; but what if you don't want to go the P4 route, but still want something very overclockable? Intel's Tualatin core for the Pentium 3 and Celeron has turned out to be an incredible overclocker as well, with 50% overclocks on the lower speed chips not too uncommon."