OS X :: Trying To Hook Up External Monitor?

I'm hooking up an external monitor to my 24" iMac. It's being hooked up DVI, problem is, when it's plugged in, the picture on the Dell monitor I'm trying to use just jutters and shakes. I tried different resolution options and none worked, most just left the Dell monitor black. I calibrated the monitor and that stopped the shaking, but when I look at the monitor everything is too big and there are still tons of "bright" pixels in the background, along with some faint lines..it just isn't right.