Ubuntu Multimedia :: Output Over Hdmi Is Too Large

im running ubutu 9.10 with the standard nvida proprietry drivers as a media center. the output is over hdmi, through a a/v reciver and onto a lcd television. my proble mis that the output is too large for the screen even whan outputting at a smaller resoultion than the native resolution of the television. this means that the top, bottom, left and right of the output is chopped off. in windows i can adjust the size of the output useing some sliders to get the image to fit the screen. however these are only available in the windows drivers and i cannot find a substitute in the ubuntu ones. one way of doing it may be to output black bard at the sides of the screen but i have no idea how to do this.