I upgraded a Server 2003 64bit box to Server 2008 R2 standard. The server is part of a domain and is not the domain controller. The network works-- I can login at the console and see the internet. However, XP workstations and other Server 2008 boxes can't access shares on the new server. MS SQL 2008 (SP2) running on the server is up (works fine from console), but it too is rejecting all external windows authenticated connections. Pings to the box are also lost.
It looks like the new box came up with a very tight firewall running, but as far as I can see, firewall is disabled.
Further background-- the domain controller is a Server 2003 box (tree has been maximally upgraded) and it has no problems with other 2008 R2 boxes.