The TV will show you what the resolution is of the video signal that it is sent. If the connection you made has 480 on it, what you see will be only based on that.
Aso, only HDMI or Component connections can carry 720 or 1080 high def signals.
Also, if the set top box or dvd player is set to send out 480, that's all the TV will see. My Comcast set top box has the adjustment to change the format.