Beta 1 of Office 12 will be available in "a couple of months". If you want to register to join the beta, go to
http://beta.microsoft.com, sign in with your passport, and then use GuestID: PDCOffice (it is case sensitive). Then just fill out the survey and wait.
Read the complete post at http://www.dotnettipoftheday.com/blog.aspx?id=60