Migration Plan from Windows 2000 to Windows 2008 R2

Hi all
I am working now to planify a migration from windows 2000 to the last version of windows 2008 r2.
We hace a head office with 8 branch with around 16 server in AD Windows 2000.
I would like to migrate to W2008, but I know is not supporting from W2000.
Head Office have:
1 PDC and BDC
8 Branch have 1 BDC and 1 Files Server and Print Server
What is the best way to migrate, I dont want to change the DOMAIN NAME, I would like just to PROMOTE SERVERS by intalling news server on HEAD OFFICE and also promote BDC in the 8 remote branch site…. In all site I have DHCP AND Dns servers.
Please give me the best practice to migrate that… I have a short time to planify this…
Thank you very much for your help.
Ricardo Bonilla
Network Admin