ATI x700 Pro to HDTV. Help with the nightmare!

Setup: I have an ATI x700Pro in a new HP computer running MCE 2005.
The card is attached to my Sony kp46wt510 rear proj TV via the dvi out
on the card and dvi in on the tv.

Problem: The image on the screen is crisp, but overscanned and neither
ATI controls nor MCE will let me go above 640x480.

Alternative: Using the s-video to component adapter that came with the
card, I can get the image size adjusted perfectly on the TV, but the
quality is terrible (I can hardly read the text).

Solution: ...................?

Thanks,

Doc