I just found this thred:
http://forums.xbox-scene.com/index.php?showtopic=486383

If you have an xbox with xbox media center running (modchip or flash hack required), then you can download the app from the thread and control xbmc using a WM5 or WM2003 device.

Visit MyPDA

I do have XBMC runnin on my modded xbox. This is gonna be sweet! Thanks for posting..

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You dont even need a 3rd party app to do this, if you load up XBMC and go to the settings and enable "web server" you can just type in your xbox IP, into IE on your PDA and take control! XBMC must be running first