You need to give more specs on your ram too. Ram plays a major role in OCing. As for the cpu, you might be able to squeeze another 100-200mhz out of it.
Just go into your BIOS and find the menu that has clocks and frequencies or cpu frequencies or something along that. Under FSB or Front Side Bus there will be a smaller frequency around 133MHz (i think thats what xp 2400 run at) raise that only 2MHz at a time, even 1 to be safe. Keep doing this until your temps start getting too high. But we need the ram specs too. Value ram wont give you much room to OC.
There is also Kangaroo's guide to OverClocking on this forum if you haven't read through it: