According to a member at the MyDigitalLife forums, the latest build they have acquired is build 8141.0.winmain.111021, which was compiled on the 21st October 2011, and includes Windows Media Center.
This build contains a number of different changes, such as changable Metro backgrounds, App zooming and more. Build 8140 has been made available in Simplified Chinese to OEN providers, the build was compiled on October 20th, one day before 8141 was compiled.
There’s no word on whether Windows Media Center will make it into the beta, but a member of the MyDigitalLife forums said that the current version of Windows Media Center is still the Windows 7 one, and has not received any updates, yet.
Of course, take this with a grain of salt. Until we see something concrete, this is only a rumor.
Further reading: beta, Microsoft, Windows 8