Thanks.
It worked for the Video, which I had edited in Sony Vegas.
However, for the photo slide show, I created this in another programme and is already rendered as a MPEG, but without music.
I went into Sony Vegas and loaded the slide show.
I then added the MP3 with the music track and rendered the music track with the same file name as the slide show and converted it to AC3.
However, this does not work in DVDA.

Do I need to re render the slideshow with the music in Sony Vegas as a MPEG again to associate the music file with the video?

Many thanks!