31" LED as PC monitor - display issues!

Hi!
I have a custom HP, i7-870 cpu, Radeon HD 5570 gpu, 8 gb ram. When connecting it to my Sharp Aquos 46" LCD via HDMI the picture is clear, no pixelation, no adjustments needed. Just connect the two and done.
When I connect my Samsun 31" LED via HDMI - no good. Aspect ratio is shot and display quality is awful. I changed from HDMI to HDMI/DVI using an adapter. It's better but nowhere near as good as with the larger Sharp. I've done the whole clear type thing and adjusted the resolution in the control panel of the pc. Still pixely and even viewing HD videos is still kind of sucky. What am I missing here?