If you're using FLIP software to program it the drivers are located in C:\Program Files\Atmel\Flip 3.4.2\usb folder or if you're using the Windows 7 you can use these alternative drivers here: [Register or Login to view links]
Got this from a friend with one, this should get you going:
Install atmel FLIP software located at [Register or Login to view links], then when you plug your avrkey in and it asks to install drivers, point it to X:\Program Files\Atmel\Flip 3.4.2\usb (if you’ve already programmed your avrkey before, then you will need to get it into programming mode by plugging and unplugging it approx 4 times until the light is blue).
Then open up the FLIP software, select atmega32u2 as your usb board. Then flash your AVRKey with any legal hex file. As a side note the AVRKey will work with any hex code setup for the original Teensy 1.0