When you contact me directly on these issues, and get a response to your questions, it would be nice if you followed up on the forums where you also post these questions with the answer, just so that others who browse the forums with similar questions would find the answer.
Just as a curtisy.
And the answer to his question is yes, you can select your own audio files for creating Slideshows. But when it comes to sharing slideshows, you can only use the audio files provided by Nero PhotoShow, as we have no way to confirm if you have the rights to distribute that audio file as we do with the audio files provided by Nero Photoshow.
In the same window where you select the audio files provided by Nero PhotoShow, at the bottom left of the window is an option to add your own MP3 audio files.