A poster on the GA Forum is claiming that Windows applications can be run on the Xbox 360 via Media Extender.
The poster, who goes by the name of Rhindle, wrote: "I was messing around with the Media Extender interface on the X360, and noticed that the "More Programs" linked to a couple of apps installed on my PC as part of the Media Center Package, including MS Instant Messenger and some other stuff.
"All of these run when you access them from the 360 Media Extender client. The 360 essentially seems to act as a dumb terminal, interfacing with the application running on the PC."
Rhindle then discovered that it's possible to integrate Windows applications via the "More Programs" tab - "All you have to do is build a link in a format specified by Microsoft and do some minor optimisation, and the app will run in MCE."
According to Rhindle, most of the apps tried "run perfectly", but the machine doesn't do so well with shareware games. "They all launch on the 360, but crash soon afterwards," Rhindle stated, adding that a bit of optimisation might do the trick.
You can read more over at the GA forum.