A word of warning:
If you plan on playing Halo 2 on a laptop or with an integrated graphics card/chip you also have to know that it might not work at all, even after all these tips and suggestions because, simply put; Halo 2 doesn't like laptops (or integrated gfx cards/chips) - It hasn't been tested thoroughly on laptops and certainly not optimized for them (again, integrated gfx cards/chips). Any integrated graphics cards (Nvidia GeForce 6150, ATI Xpress 200, etc) will not run Halo 2 well. But usually this is the case with all games, right? Well let's not forget that Halo 2 is a port...
You know, the sticky's there for a reason...