Its called 'RGB Shift' or 'RGB Push'. For some reason when using an RGB lead for everything, it pushes the image to the left/right a bit. You can only fix it by disabling RGB or if your TV allows adjusting the image, either via the service menu or by a normal onscreen menu.
That may be your problem mate. What blackbolt has said is true-ish, as not all rgb scarts do this. My official MS 360scart doesn't, nor my new ps2 scart, however my old ps2 scart did. Just need to go official methinks.