Polaroid FLM 1507 LCD HDTV Monitor/TV

Hey guys i opened my LCDTV and i hooked it up to my PC via a Component connection, heres where my problem is. I get a picture, but its not full screen, whenever i change the output i get like smaller images, and it goes back whenever i revert to the 480p. 480p was the initial setting. At this setting i can only view like 1/4 of the desktop so in order to view the rest i would have to move my mouse over to the other corners of the screen. What the bloody heck is going on, i know it has to do with my Videocard, BTW i have a ATI RADEON X800 XL PCI EXPRESS X16 card. So far im using the VGA connection, but i want to use the full power of my Display, can anyone help me. PLZZZ Thank you