Microsoft has confirmed that Xbox Live will be integrated in Windows 8. There was a rumour for a long time, and it has finally been revealed now. Major Nelson had this to say in his blog.
We are confirming that we will be bringing Xbox LIVE to the PC with Xbox LIVE on Windows. We are very excited about Xbox LIVE coming to Windows 8. Xbox LIVE brings your games, music, movies, and TV shows to your favorite Microsoft and Windows devices. Bringing Xbox LIVE to Windows 8 is part of our vision to bring you all the entertainment you want, shared with the people you care about, made easy.
At BUILD we are showing that it is easy for developers to create games for Windows 8 that take advantage of the power of Xbox LIVE. We have much more detail to share about the capabilities of Xbox LIVE on Windows and look forward to the opportunity to do so in the near future.