The timeline creation was the problem. THANKS! (Menus linked immediately after import, so I assumed video assets would do the same. I will now beat myself severely over the head with the Encore manual by way of expiation.)
I'll test output to DVD with the current menus (which work in simulation mode), because I have a lot of time invested in the artwork (which has to match print- and computer-screen products). Worst case (I hope) is that I use PS's NTSC DV preset to build a new PSD file and then copy my current menu layers.
These Adobe forums are life-savers for those of us who bounce from app to app with every project. Thanks to all of you who share your expertise.