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 (camspace.com 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 
http://www.youtube.com/watch?v=s7MKAj7bon8