This is a simple project which converts your normal computer monitor into a touch screen monitor.
I have used two SRF005(ultrasonic range sensors) to measure the X and Y distances of the obstacle(finger or a pen) and picaxe 28X2 sends the two values to the computer.
In the computer VB .NET receives these values through the serial port and makes some calculations to get the exact point on the screen. Using these values the mouse pointer is moved to the corresponding point. Clicks can also be simulated with the VB .NET code.
For more pictures and videos please refer to the attachments section in my letsmakerobots.com link.