There are actually a number of ways (at least 4) to create a slideshow in Premiere Elements, and without knowing which of those methods you're using it's hard to comment specifically.
But if you're building your slideshow on the Premiere Elements timeline, first make sure you're in Timeline mode. Then, when you add your audio track, hold down the Ctrl key. This will allow you to place the audio on a parallel track, below the video/slideshow. If you don't hold down the Ctrl key, the audio will be inserted -- which means that it will drop onto the timeline and push all of the video/slideshow to the right -- which is what sounds like is happening to you.
BTW, the trial of the program has a number of limitations, including limitations on its ability to render. In other words, you probably won't be able to output a video or DVD of the slideshow you create in the trial version of the program. Just a word of warning before you put too much time into it.
And I would also recommend you convert that MP3 into a WAV file using a program like Audacity (free). It will save you some headaches in the long run. Also, when you see red lines above the clips on your timeline, press Enter to render the timeline. (When rendered, the red lines will turn green.)
Lots more headache-saving tips like this in my books, if you're interested.
Thanks for your reply. I've found that Windows Movie Maker does what I want to do so I think I'll just use it. Fewer headaches.
Glad you found a solution, aces.
There isnt any render limitations in Trial version. You can simply drop your audio to Audio track and not along the slides