The company achieves this feat by selling custom-designed pressure-sensitive resistive touchscreens in two flavors: an external model that attaches to the iMac and a factory-installed internal touchscreen. Being an Apple-certified Value Added Reseller allows Troll Touch to offer Apple’s standard one-year warranty on the modified Macs and it's been doing this since 1987, so it must be pretty good at it by now.
If you own one of them fancy new widescreen 21.5-inch or 27-inch iMacs, you can have a touchscreen installed on it for $1,099 or $1,699 respectively. Alternatively, you can buy a new iMac directly through Troll Touch and have it outfitted with a touchscreen before it's shipped to you. Troll Touch offers four different iMac configuration choices if you want to go that way, but you don't get to customize the model like you do on the Apple Online Store. Troll Touch also offers similar solutions for older iMacs, Cinema Displays, and MacBooks (including the most recently-launched models).