Well, its not exactly windows but it does run .exe's and support drivers designed for nt and xp, currently its in it Alpha stage but best of all

OPEN SOURCE

http://www.reactos.org/en/index.html

Yup, ReactOS has been bootable on the Xbox for some time using a modified version of Cromwell. See http://www.reactos.org/wiki/index.php/HOWT...ReactOS_on_XBox (and search for 'xbox' on reactos.org).

Last I checked there was no driver for the nForce ethernet controller, though, which means once you boot ReactOS you can't get to the network.