Do you care more about quality or performance, because here is a simple way I got Halo from lagging on minimum video settings, to being able to run almost maxed out:
Note: You MUST have an NVidia card to do this!
1. Download nVHardPage here: http://www.nvhardpage.com/modules.ph...op=getit&lid=2
2. Unzip/rar it, and run nVHardPagese.exe
3. Go to the tab with the NVidia symbol
4. Scroll all the way down to the bottom
5. Unless it is already checked, check the box that says override vertex shaders.
6. Change the bar just above the check box to the left until it says 1.1
7. Exit, and this should increase performance with games using directx
Note: If you want, you also can screw around with the antialiasing modes and overclocking, but I'm not going to cover that now.
Hope this helps ya!