Both suggestions for adding deinterlace to avs script, bob() and FieldDeinterlace(), worked in my tests.

But the resultant video image (in this case a skvcd template at 480 x 480, with both video stream and source aspect ratios at 16:9) was squashed/flattened somewhat. When I encode using TMPGEnc without the avs script this does not occur.

My TV is not widescreen, thus on my DVD player I set it to TV = 4:3. If I set it to TV=16:9, then the video image from the avs script looks fine. But at that setting normal DVD images get stretched taller. What is going on? Something I don't understand, I'm sure.

You will need to set the aspect ratio under the Video tab to "4:3 525 line (NTSC)". Under the advanced tab, set source aspect ratio to "16:9 525 Line NTSC" and the Video Arrange Method to "Full Screenv(keep aspect ratio)".