The main idea: a user creates a powerpoint file with 1 slide, and this slide is inserted into a slideshow which is already looping. A first idea I had was to convert the .ppt file into an image (e.g. using http://www.artofsolving.com/opensource/jodconverter/ or a .NET API), and then create a flash application which scans a directory for images(/converted slides) to show.
But this seems a bit like a complex solution, any suggestions?