Works great, and as said before it is THE best PC gamepad out there.
You need either the wired controller or a wireless controller with the adapter, if you already have a controller you use with your 360 you can use that. I don't have much experience with the wireless version and a PC, but I use the wired version with my laptop daily. Do NOT buy the PC version of the controller, it is the exact same controller with a useless CD included. Buy the normal 360 wired controller. There is no difference between that and the PC version except that it doesn't include the driver CD. You can get the drivers off of Microsoft's website.
If you have Windows Vista....
1. Plug in the Controller
If you have XP....
1. Download the driver here: http://www.microsoft.com/hardware/gaming/download.mspx
2. Install Driver
3. Plug in Controller
It's pretty simple. I use mine with Sega genesis and SNES emulators and it works great.