My Hidef Tivo has a coupla USB ports on the back of it "reserved for future use"
I would think streaming/data transfer might be one of the future uses.
You can actually order Media Center edition OEM now
I also got a copy through our MS Partner program, but haven't had a chance to do anything with it. The HDTV capture cards appear to be pretty tweaky, too.
I played around with a HTPC - never could get the Windows desktop to look even decent on my HDTV, even with the Radeon HDTV adapter.