Over last few weeks, we have seen several cases where our customers wanted to remove the last Exchange 2000 or 2003 server from the Exchange 2007 organization and were not sure how to accomplish this.
I wanted to let you know that we have updated Exchange 2007 Server Release Notes today to include this information. You can find Release Notes here. To see this specific information, search the relnotes for "Workarounds for Selected Known Issues" and then scroll down. We broke this in two sections:
How to prepare to remove the last Exchange 200x server from an Exchange Server 2007 organization
How to remove the last Exchange 200x server from an Exchange Server 2007 organization