http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=fa629de2-f4dd-47ac-8d80-3db46b2877a2 is the how to upgrade an existing pre Server 2008 or 2008 R2 domain to 2008 or 2008 R2
Just finished http://www.betanews.com/article/Mark-Russinovich-on-MinWin-the-new-core-of-Windows/1259792850 by Mark Russinovich which is very interesting and shows how much better 2008 R2 is over say 2003.