Well if it is a wired controller just plug it into the USB port. If it is a wireless controller you will need a XBox 360 wireless receiver for PC.
http://www.amazon.com/Xbox-360-Wireless-Gaming-Receiver-Windows/dp/B000HZFCT2
http://www.newegg.com/Product/Product.aspx?Item=9SIA0U00921743
Although these do not seem to be made by Microsoft they should work. I will see if I can find a genuine Microsoft version and update when I do.
Either one of those should work for wireless. Of course you can get the XBox 360 controller for Windows that comes with the controller and usb receiver or at least I think there are still for sale that is how I got my first one and the rest I just got the XBox 360 versions as they work with the USB receiver just fine.