Upconverting . . . where?

I have a Sony XBR LCD set and a non-upconverting DVD player.  Is the
TV automatically upconverting the 480p (I can select progressive on
the DVD player) to something better?  The picture seems fine, but not
noticably better than what I saw on my older CRT.  DVDs have always
been crystal clear.  Is there something to be said for the
upconverting capabilities of newer DVD players (e.g., the OPPO
discussion with its higher-end circuitry)?  Thanks.