I don't believe without any hardware you can use any display as touchscreen. As u said u need "Compatible device" i.e, you need touch screen to use it. And the device i told is being sold on ebay. So, just buy one and there u go.. Enter the matrix..
Here is some links for those products
http://trolltouch.com/ (Toooo costly)
http://store.earthlcd.com/LCD-Produc...ch-Screen-Kits (Cheaper)
I want one of those.. but $270 for 15 inch??? :shok: