As jimsowden pointed out, overclocking the graphics card is simple and easy (I assume you're talking about usine ATIcceleratorII, right?). Just keep upping until you find you're getting artefacts, then back off a couple steps and test, test, test until you find a stable point. But keep in mind, Apple laptops are pretty set for heat, so it's going to make your card run hotter and can, in extreme cases, melt it, which is bad on a mbp as (I assume) it is onboard...