Yes I could do multi touch especially if I would surround my camera with infrared LOD would replace its infrared filter with a filter for the visible light and put the whole thing behind my monitor

This may helps you a little:
http://msdn.microsoft.com/en-us/library/bb205353(VS.85).aspx
http://www.cs.nps.navy.mil/people/faculty/capps/iap/class2/viewing/projection.html
You will have to build an off-center projection matrix depending on the viewers position. You may also have to move the view a little for good results, but I don't really know. It isn't very easy, at least not for me and I think that you won't find too much help.
I haven't tried that yet and yes that matrix is used in a vertexshader but I would recommend you to just manipulate the engine matrices in a material or render event.