Actually it makes no sense to upconvert if you are using a CRT. The best way to view an image with a color resolution of 720x480 is at 720x480. Upconverting it to 1280x720 or even 1920x1080i does nothing to improve the image. It will alter it for sure but you can not add detail that was not there to begin with.
The only benefit of an "upconverting" DVD player is if the scaler in your fixed pixel high resolution display is terrible. For example a DLP TV with a native resolution of 1280x720 will use 1280x720 pixels to display the image wide screen no matter what the source. The DVD has to be scaled at some point between the data on the optical disk and the image that reaches the viewers eyes. Most modern TVs can do this adequately on their own. However if you know for sure that the scaler on your DVD player is superior than the scaler on your TV then it makes sense to use the DVDs on board scaler.
On the otherhand I don't really know of any DVD players that have such superior scaling. Sure they tout upconversion but they don't specify what kind of algorithm they use whether it be bilinear filtering, bicubic, lanczos, etc. Upconversion with a DVD player is really a marketing gimmick for the most part.
