Currently we are running Win2k3 SP1, R2, SP2, Win2k8 Beta3, RC0, RC1, and RTM Escrow idomain controllers in production... Since we're running some downlevel servers in the environment and I was interested in what is supported to be upgraded to Windows 2008 when we sign off and the the DVDs start getting pressed. Luckily a mail came by on one of our discussion aliases that has the details I (we) desire.
Upgrading Active Directory Domains to Windows Server 2008 AD DS Domains
What Service Packs can be upgraded to Windows 2008