it runs them fine for the most part. I only installed HL2 just to see it run mainly because gaming on laptops is not my thing. My laptop is my work computer.
I saw a demo of a Mac Pro (desktop) running battlefield 2 and it ran it very very nicely. Those dual xeons killed that game.
You could even probably run CSS on the macbook's integrated graphics chip it just wouldn't run all that great.
Plus you have to get a program that runs windows to run windows based games, then you need a windows OS.
You cant just pop in a windows OS.
You need another program to allow that.