Thanks for the suggestion, but that didn't work. It draged both the audio and the video tracks. What did seem to work, was selecting the first picture, right click and select to end, then group, then hold down the ctrl key and drag. However, it seems each picture has a limit of 25 sec. ???

You're right: CTRL+A also selects the audio. My mistake.
Next, the 25 secs limit: well, you have to consider if people want to watch a single picture that long without getting bored - even if the music is ok! Also, this method (the dragging thingy) doesn't allow exact timing, which makes an exiting experience: timing transition to music beats/shifts.
So in my opinion, you should time the picture show to the music in an interesting way, and cut and fade the song when the pictures end.
If for some symbolic reason you want to play the whole song, you could introduce picture enlargements, and pans and zooms, rather than showing pictures for 25 secs or even larger.

Actually it's not a 25 second limit. Pictures can be as long as you wish. However, that stretching method has a 4x limitation. You can only stretch events out to 4 times their original length or squish them to 1/4. Since the default still image length is 5 seconds, this means that the stretch/squish method gives you a range of 1.25 to 20 seconds. As Ivan pointed out, if you have still pictures that last 20 seconds or more then you probably need to rethink your slideshow, make it shorter, or add more pictures.