This wireless receiver product description on amazon specifies that you can use up to 4 wireless controllers with one single receiver.
To pair multiple controllers to the same receiver, simply follow these instructions for each separate controller.
To summarize the instructions:
  1. Plug in the gaming receiver to a USB port on your computer
  2. Use the "Install Automatically" option if the Add New Hardware wizard pops up
  3. Download the XBOX wireless controller software from here and install
  4. Once installed, turn on the controller by pressing the middle 'X' button
  5. Press the connect button on the receiver (the light flashes green)
  6. Press the connect button on the wireless controller (pictured below).

Your Xbox wireless controller should now be connected to your machine. Repeat steps 4-6 for each additional controller.