hi i had the same problem but mine is a hitachi
this worked for me .When in pc mode with the picture from the computor can you press the analogue menu or the one that gives you the brightness and contrast controls for your tele if you can scroll down the list and seeif it lists   WXGA on mine it is upto 800X640 when off and a variety of wide screen options when on
check your manuel for   W.X.G.A. HOPE THIS HELPS by the way it does not make any difference to the telly side what you do on the computor as long as you have a wide screen aspect on it