Hook up XBox to monitor without signal degradation?

I have a Dell WFP2007 that accepts s-video in. I plugged my old XBox (pre-360) into it by converting the XBox’s yellow composite jack to s-video via adapter and the remaining red and white audio cables to a standard line-in via a y-cord. (Pretty standard.)

Everything works, but the XBox video quality suffered somehow. I don’t know what I’m doing wrong – should I set my monitor to a different resolution? Or do I need to change a setting on the XBox?

Thanks a lot! <3 Fluther.