Thanks.. I had tried that with the composite video cable and the optical digital, as you suggested. Substituting component cable was going to be my next step, but first I took the CT-500 manual to bed with me and studied it more closely. The instructions were there in black and white. "Converting the resolution of analog video input." I still didn't understand it but I looked more closely at the "GUI Menu" on the CT-500. I tried various menus and then saw a downward carrot at the bottom of the screen which led to several options I hadn't seen before which led me to a video settings menu that allowed me to select 480/576p instead of "auto" which had been the default setting.
Voila! or rather D'uh!
RTFM AND try everything.
When I switched back to CATV input the unit automatically switched back to its automatic setting, showing the wide screen view. I was interested to see what the menu would show for those options. Since the CATV input was HD, it did not show the options but simply said "not in use." When I switched back to the DVD the 480/576 setting had been retained. I don't know what will happen when I try a different DVD, but at least now I know where to go to change it.
Thanks both Robert and Matt for your patience and help.
By the way, the test DVD was of a live theater performance of Hamlet with Richard Burton. Watching it in proper aspect was with the CT-500's speakers was wonderful. I had seen the performance live when I hitch-hiked to New York for the World's Fair in 1964. A short fat Burton would not have been the same.