Points to consider for an upgrade
Windows Server 2003 R2 includes User Name Mapping. Windows Server 2008 does not. Upgrading to Windows Server 2008 removes the User Name Mapping service.
Windows Server 2008 can still retrieve UNIX-style identity data from remote User Name Mapping servers. Windows Server 2008 can also retrieve UNIX-style identity data from Active Directory Domain Services (AD DS). Customers can either set up a centralized remote User Name Mapping server or integrate UNIX-style identity data into AD DS.
Anonymous access in Windows Server 2008 is handled differently. The Network Access: Let Everyone permissions apply to anonymous users security policy must be set to enable anonymous access.
Customers need to ensure that Windows Server 2008 firewall settings are still valid after migration.
Services for Network File System (NFS) in Windows Server 2003 R2 requires that you manually configure the Windows Firewall. In Windows Server 2008, this is not necessary.