Menu Background Image Problem



I have a problem with the ‘Convert X To Dvd’ program that is driving me crazy!
If I want to use another pic for the background image in the DVD menu, sometimes it works and other times it doesn’t.
If I use the video preview, I can see the image there with the titles, but when the burn is finished, most of the time this is replaced with the generic black or blue image instead.
What is the criteria for using images; should they be only jpg’s or gif’s?
Shoud they be resized to the same size of the included bg images?
Am I doing something wrong?