First of all, you should probably have someone tell you that gaming on a laptop is not really recommended. Laptops have stripped down versions of their desktop counterparts so that they run cooler and are easier on the battery. The screens generally have lower response rates than desktop LCD monitors, so ghosting effects are much more likely, and you can't do much more beyond upgrade the RAM for hardware upgrades. Then there's the cramped keyboard, and relatively small displays with fairly low maximum resolutions... It all adds up to a very poor experience. I'd recommend a Nintendo DS and/or Sony PSP if you want portable gaming.
If you need to find out for yourself, the answer is still the same. ALWAYS, ALWAYS, ALWAYS get the best possible laptop you can afford. Since you are generally stuck with whatever the thing ships with, ALWAYS get the best possible specs you can in every way. That way you increase the odds that the system will last for a while.
Im going to buy a MacBook pro and had a questions. Will it affect gaming much if i opt to go for the cheeper NVIDIA GeForce 8600M GT with 256 MB. Or is it a must for the 512 MB? Im not going to be playing games on max settings but want it to look nice.