I just hooked my Sega Dreamcast up to my PSone screen via a composite cable. The image comes in ok, and the screen powers up nice. My problem, is that the picture is not centered, and there is a border of black around the whole image. Note that there is a bigger black border on the left side, than there is on the right. When the Dreamcast first boots up and through the first couple intro videos, the screen has no black border, but as soon as you are in game, there is a black border. This has happened in every game I have tried so far.
Would this be because I am using composite? Anyone know what's wrong?
Sorry this is the best picture I can take (no camera atm).

Thanks in advance,
Nathan