Microsoft started with a beta as an answer for Joost.  It's called Livestation.  At this moment only a few people can test it, but later this year they will invite more people. One of the advantages of LiveStation is that users not only can look to On_Demand, but also Live television.

The architecture uses just like Joost the P2P technologie.

So I'm looking forward to test LiveStation and give a complete report about it and the differences with Joost.