You'll have to be careful what northwood core you get, you probably have a northwood A there are b and c varients which probably also are not supported by your chipset/bios.
edit: Supports one Intel® Pentium 4 processor, up to 2.8 GHz, i845E 133MHz FSB (533). So iirc that would mean you can use northwood A up to 2.8GHz or B up to 2.66GHz