We have an existing Windows 2003 server running Exchange 2007 and a Windows 2003 domain controller. We have two Windows 2008 servers loaded with all MS updates and would like to perform an upgrade of both the domain controller and the Exchange server to Exchange 2010. The Exchange server is running out of space and there have been some issues with named properties quota being maxed out so we would like to replace the Exchange server first. Both servers are on the domain, the new DC being a member server for now, and Exchange 2010 has not been loaded on the other server as of yet. Ideally, we would like to install Exchange2010 on the new server while keeping the old Exchange server up and running, then move mailboxes at our convenience. Is there a best practices process to get this done? Also, do you think we should upgrade the domain controller first or does it matter?