Someone managed to boot Windows 98 through XDSL on the xbox a while ago. So by first booting linux on it and thereafter launch windows.
However there are not real drivers for almost anything in the xbox so it is not running efficiently.
Here's some info for you:
http://forums.xbox-scene.com/index.php?showtopic=279664
A complete tutorial on how to get Win 98 to boot:
http://pspold.qj.net/windows-98-on-xbox.html
A little more:
http://forums.xbox-scene.com/index.php?showtopic=380167
However if you really want some sort of pc functionality on your xbox I would recommend you to use any xbox linux dist instead as they have been optimized and tweaked for the xbox.