Microsoft Exchange 2010 Installation Rediness check.

We are installing an exchange 2010 server into an existing domain, which has 2 x 2003 Exchange servers and a 2008 domain controller.

 We want to migrate the mailboxes to the new single exchange server.

 When we run the installation during the readiness checks we get the following warning.

Warning
Setup is going to prepare the organization for Exchange 2010 by using Setup /PrepareAD. No Exchange 2007 server roles have been detected in this topology. After this operation you will not be able to install any Exchange 2003 or 2007 servers.

No this cared me to death, as we do have EXISTING 2003 exchange servers in our domain, and we want to migrate the mailboxes to the new exchange server.

Firstly, has this process already done this, as the Readiness check failed, ie does it only proceed with setup /PrepareAD when all the checks complete successfully.

Secondly, if it does do what it says, is it going to stop us using the existing Exchange 2003 servers, as we are not ready yet to migrate. I just wanted to install our new exchange server and migrate a couple of test mailboxes for trial.

Obviously to do this we need access to both the Exchange 2003 servers and the new Exchange 2010 server.

Any help much appreciated.