All you have to do is buy a magic pen called as Portronic Handmate Windows 8 Pen. This Pen after a very simple configuration starts acting like a stylus.
The probable logic behind its working is it adjusts to your screen resolution and based on your distance from the left senor calculates exact position where you have touched on your screen.
This gadget is really good for all those who don’t wont to spend a lot on touch screen devices yet want them. This device I think does not convert your screen into touch screen all it does it tries to mimic your stylus as though it is actually touching your screen.
Its great for people who do lot of PPT presentations and want more flexibility than mouse. Below video will give a very nice demo of this product. this device is built only to work with Windows 8. Its avaiable in India foe Rs 5000 only.
You can find more information about this device here http://www.portronics.com/handmate-windows-8-pen.html