Windows Drivers for the xbox controller are available here.
http://www.redcl0ud.com/xbcd.html
or direct link to the installer http://www.redcl0ud.com/files/XBCDv107.exe
The xbox controller is regular USB with a proprietary connector on it, so it's super simple to convert the connector so that it can be used for both the xbox and a computer. If you already have an extra USB cable laying around, and a soldering iron, it's free. Or you can buy an adapter, but the soldering method was best for me as I had tons of extra USB cables when I did mine. I did this quite some time ago for using emulators, so I don't have my own pictures of the soldering etc but I do have my finished project.
Some instructions have you cut up a connector, which is a waste when you can just open the proprietary xbox connector on the end and still use both.
There is a better guide somewhere on the internet but this is basically the same thing.
http://www.ocmodshop.com/default.aspx?a=223
Here is a picture of how mine ended up.
If they disable hotlinking, http://bayimg.com/JaeNnAaBc
And here is a much higher resolution image if you want.
http://bayimg.com/IAEnhaabC
And this is the pinout of the xbox connectors.
http://bayimg.com/KAeNCaABC