Many thanks for replying. When I insert the dvd, the title page comes up, but I see no thumbnail image. Just out of curiosity, I went back to the Roxio burn menu, where the thumbnail image can be find. "Enter" doesn't have any effect.
I'm not sure where to find the right thumbnail. I looked in Finder, too, and found lots of VTS files under "video", but these had no effect. I tried clicking on the DVD icon on the Mac desktop which simply gave me a list of the contents.
One development, I discovered (blush, blush for not having invested better earlier) Toast 11's conversion function and used that to convert the flv file. The preview function reads the converted file without problems, but the DVD, also tested on a Win machine, doesn't want to start.
Thanks in advance for any solution you might be able to provide.