Coexistence with Exchange 5.5 is the most complex scenario handled by ExDeploy. The ExDeploy experience for coexisting with Mixed Mode Exchange 2000 and Exchange 5.5 is very similar. This scenario is broken down into two major steps.
Upgrade the ADC servers.
Install or upgrade the first Exchange server.
Upgrading the ADC servers in a PtOz organization is a multistep process.
 PtOz refers to a Mixed Mode environment containing Platinum (the code name for Exchange 2000) servers and Osmium (the code name for Exchange 5.5) servers.
Verify that your Exchange Organization meets the Exchange 5.5 coexistence prerequisites previously described.
Run FORESTPREP ...