Not the best kept secret I know (and so do you all by now), but the press release is here,

In summary, Virtual Server 2005 R2 will become a free download, in effect there is now only the Enterprise edition, so 1-32 CPU's are supported on the host server.

The second part os that these Linux distributions are supported:

  • Red Hat Enterprise Linux 2.1 (update 6)
  • Red Hat Enterprise Linux 3 (update 6)
  • Red Hat Enterprise Linux 4
  • SuSE Linux Enterprise Server 9
  • Red Hat Linux 7.3
  • Red Hat Linux 9.0
  • SuSE Linux 9.2
  • SuSE Linux 9.3
  • SuSE Linux 10

In addition "Microsoft continues to license royalty-free the Virtual Hard Disk (VHD) format of Microsoft Virtual Server. There are now more than 45 vendors signed up in this royalty-free license program" this is large increase over and above the original supporters of the VHD format.

John has additional details here and here as well.