They can, if you're lucky... I've got two old MMX 200Mhz systems and one P1@166Mhz, and I can't verlcok any of them because their BIOSs won't let me tweak the frequency settings.... the older the hardware, the lesser the cahnces you can actually get in there to tweak it...
Ahhh! It's 2003 and wait, whats this!? My computer didn't blow up! ... Well damn, there goes my new Athlon @ 333FSB and my inssurance claim... heheheh