As of this writing, co-existence with Exchange 2007 and Exchange 2013 and Exchange 2010 and Exchange 2013 will come later on.
No co-exitence with Exchange 2003 is planned, so get to 2010 asap.
Right now, if you want to play around in your lab, you are somewhat limited. Remember no co-existence is supported at this time, but some work can be done if you’re just looking to learn.
Installing Exchange 2013 into a Exchange 2013 organization isn’t possible.
the installation stops with an Error that says “Exchange 2013 all exchange 2010 servers in the organization must have Exchange 2010 Service Pack 3 or later installed” and points to this.http://technet.microsoft.com/library(EXCHG.150)/ms.exch.setupreadiness.e15e14CoexistenceMinMajorVersionrequirement.aspx
So no playing around for the Exchange 2010-2013 configurations until Exchange 2010 SP3 is released.
Installation into an Exchange 2007 org went as planned.
Note a warning stating no Exchange 2010 can be installed into the organization after the Exchange 2013 setup was complete.
A few notes on the installation. I installed with the Administrator account which had its mailbox on the Exchange 2007 server. This meant that I couldn’t open the Exchange 2013 ECP. To fix it, I created a user in AD with the appropriate permissions and ran the enable-mailbox command from the Exchange shell. I’m sure I could have also run the New-MoveRequest command and moved a mailbox as well.