I'm going to show you how to enable Anisotropic Filter on Halo. If you don't know what it does then take a look at this pic
http://img855.imageshack.us/img855/3187/m4wi.jpg At the top you see original halo, at the bottom you see halo with anisotropic filter (note the ground textures). To enable this, open config.txt from your halo ce folder and look for your video card. If you can't find it then look for "Unknown". Under your video card there should be this:
//UseAnisotropicFilter
if os < Win2K
if driver < 4.14.10.4467
LinearTextureAddressing
endif
if driver < 4.13.01.4071
OldDriver
endif
if driver == 4.14.10.4524
LinearTextureAddressingZoom
LinearTextureAddressingSun
endif
endif
<...>
Just remove // and save the file. If you want to disable it then add // again.