iPad as mobile smartboard?

I want an iPad, but I want one because I have a wild fantasy that it will do something it might not be able to do.

I want to use an iPad like a mobile smartboard. I teach at a university and would like to be able to walk around my classroom while presenting a lesson (on ppt, keynote, word, what-have-you), but while maintaining the ability to freehand manipulate that presentation like I can with a smart- or starboard. I want to stand in the back of my classroom with my ipad and circle or write a note on the presentation in response to my students and have the iPad wirelessly transmit to either the computer connected to the projector or to some receiver attached the VGA cables that feed the projector. Does such a receiver exist? Is there an App for that?

I'd love to see Apple work on a mobile presenter like this; university instructors and researchers are such dedicated Apple customers, and we get such lovely technology budgets (even during debt crises).

I don't know of any way to do this wirelessly, but I share the same dream. To be able to hand it to a student (to edit a piece of writing, work out a problem, annotate a website--tons of possibilities) and then have her hand it back, or pass it along to another student. It would really enhance the class.