Instructions
Wired Controller
Plug your Xbox 360 controller's USB charging cable into the top of the controller you want to use on your PC.
Connect the USB input on the opposite end of the same cable to a USB input on your computer.
Download the Windows XP Xbox 360 controller device driver from Microsoft's website (if applicable). If you're running Windows Vista or Windows 7, the operating system will automatically recognize the controller. However, Windows XP users need to download the driver file from the Microsoft website and double-click it to install before using the controller.
Wireless Controller
Plug your Xbox 360 video game controller's wireless receiver (the device that resembles a regular USB flash drive in appearance) into a USB port on your computer.
Press the "Connect" button on the controller.
Press the "Connect" button on the wireless receiver. The Xbox 360 controller can now be used with the PC. Note that if you're running Windows XP, you still need to download the Windows Xbox 360 controller device driver as referenced above.