It's called ePSXe, short for Enhanced PSX Emulator. It lets you play GT2 (or any other PS1 game for that matter) on your computer just like any other PC game. You can use your Dual Shock to play, but you either need to buy a connector to connect your ol' PS1 controller to the computer or buy a directly USB compatible controller. I prefer to buy the connector, because most of the USB compatible controllers are made by thrid parties and their quality is crap to say the least. Suchayo should know more about this, he helped me a lot on configuring and finding the right drivers when I wanted to set up ePSXe myself.