But what if you are lecturing at a distance? Imagine people get to watch you by videoconference while watching your slides. How do they know when to go to the next slide and so on? The solution, I believe, is to use AJAX. With a little PHP or Python based server-side script, you could control which slide must be displayed and anyone looking at your slide show would be automatically moved to the right slide.
For extra points, make it so that the administrator can upload a picture (maybe using a webcam) which gets displayed in the right top corner, so that it feels a bit more like a videoconference.