It has been proven that multi-core computers are slower than single-core computers for games. I do not know of any major game that is written for multiple threads yet. He would be better off with a machine with multiple video cards.

I would say for a gaming laptop, stick with a single core if you can convince him, else do not go above dual core. Then look for a 7200rpm hard drive and put 2gb of ram in it. The video cards will make the biggest difference after that. Find out what resolution he plays his games at. Then try to find a screen that has that as the native resolution. LCD's look better at their native resolution.

Have fun spending your money!