In a GeForce 6600 the options you really need to consider are:
1) Anti-aliasing. Set this to "always off" or at MOST 2x. This isn't the most powerful of cards, and while it *could* do FSAA it wasn't really designed for it. It will slow down your framerate. If you get such a smooth picture that you're willing to settle a bit for better image quality, then try it out.
2) V-sync. For AH I leave this to "application controlled".
The rest you can pretty much leave default, except the "image quality" slider, that's up to you. I think I've got my at the mid-way mark, best balance between performance and quality.