Transition Single Exchange 2003 server to Exchange 2010

Hello, we currently have an exchange 2003 server that needs to be replaced. It is a DC, although we have other DCs in the domain. We also have an existing exchange 2010 server that someone tried to transition to in the past and gave up. First, how do I transition to a single server 2010 setup? What do I need to do at the firewall level? What about Active Directory? And what do I need to do at our spam filtering solution? (MXLogic) Also, the 2003 server provides DNS and DHCP, how can I transition those roles away from the 2003 server? Finally, how do I remove the remnants of the old 2010 and 2003 servers? Thanks!