Resolution Question

I'm trying to run CF at the lowest res without having it blowup fullscreen.

A little more explanation:

When I run CF at max res on my 24" monitor it looks great, but I get sh1t FPS.

So I run it on the lowest res possible, and either the game, Vista, or my Samsung monitor blows it up to fullscreen and makes it look all blurry.

So, I'm trying to get it to run at the res setting I choose, or "pixel for pixel" and don't know how.

Can someone help me?