Making a touchscreen using a webcam? Any softwares?

Is there any way I can transform my monitor into a touchscreen by using just a webcam that I can point to my monitor and detects my finger over it? Single touch would be OK.. I dont necessarily need multitouch feature..

I've heard about camspace free software ( project) but that detects any shiny objects which in turn you can use to control things like mouse cursor etc.. But I need "finger on the monitor" touchmotion and not just motion of finger in mid air.(which camspace does). if you can get what I meant...

All the information you need is in my answer :-
IR pen touchscreen software THIS