We are planning on deploying Exchange into a new domain that does not have any previous version of Exchange installed. We weren't sure if we were going to go with Exchange 2007 or 2010. While we were deciding, I read that the Active Directory schema changes for 2010 were included in the 2007 SP2 schema update. I also read that if you did the schema updates for 2007 SP2 you wouldn't have to do them again when you install 2010 RTM. I went ahead and updated the schema with Exchange 2007 SP2 without any trouble.We never installed Exchange 2007, instead we decided to go with Exchange 2010 RTM. I started to run setup on the mailbox server and during the Organization Prerequisites readiness check, I received the following 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 2007 server roles.So my question is...why does it need to run /PrepareAD if I've already run it with the 2007 SP2 media, which is supposed to include the schema changes for 2010? What exactly is this going to do?

The schema updates are not the same as the the PrepareAD option:http://technet.microsoft.com/en-us/library/bb125224(EXCHG.140).aspx Prepare Active Directory and DomainsYou'll also have to the PrepareDomain option after that as well.

Ok, but I did run PrepareAD and PrepareDomain from the 2007 SP2 media as well. Is there something different that running PrepareAD and PrepareDomain in 2010 RTM does differently than 2007 SP2?

Yes, It will create the 2010 Security Groups, apply new ACEs, check permissions etc...The link I posted earlier hasnt been updated yet to reflect the new 2010 security groups More info:http://msexchangeteam.com/archive/2009/09/23/452595.aspx