If the old dell p3 is on a 440BX board, it may still rely on jumpers for multiplier and FSB settings, in which case you can try to overclock it, or there might be a new bios for it with overclocking options. You'll really just be able to change the multiplier, though, as 440bx boards generally (not all, don't bite my head off) wouldn't even make 112MHz bus properly. Old p3's (katmais) don't usually overclock for crap, though, because they're just p2's anyway, and already at about the height of their lousy architecture. Might be able to get a 450 to 500 or so, though.