In my computer supported collaborative work seminar, we were discussing the design of table-top systems for synchronous collocated collaboration. There was a bit of conversation on the problems and strategies with images projected onto the table (e.g., people getting in the way of the beam). There seemed to be consensus that most simple and effective solution was projectors mounted directly above the table.
I pointed out that, in this context, straight down was the most straightforward.
In fact, You want the projector under the table, projecting in a back-projection like way. Then, the image won’t be disturbed by people looking at the table and leaning over it to reach to a point far from where they are seated.
It turns out that in order to sensors and such as well, it makes the table much more fragile so that it can’t be used like a real table (e.g., to put your coffee cup on it).
<A HREF=”http://www.jamespatten.com/audiopad/”>this table-top system</A> might be of relevance to your designs.
James work in the same lab as I do (the MIT Media Lab). I had dinner with him tonight and I’ve certainly played with audio pad..