A Domain Rename in Windows Sever 2003 domain, was something I never used to recommend, though it was very well documented by Microsoft on How Domain rename worked and How to perform domain rename using the Domain Rename Tool. Why get into the hassle of renaming, can we plan and design it properly in the first place. Agreed there could be many reasons why it was required.
But domain rename was not supported in AD Domain/Forest for any of the versions prior to Exchange Server 2003 SP1. Now the same is the issue with Exchange 2007. So if you have Exchange 2007 in an existing Windows Server 2003 Domain, please do not rename the Domain. Exchange 2007 System attendant will refuse to start.
Microsoft confirms the same here, so before you plan to upgrade to Exchange 2007, make sure you are aware, well if you have already updated then live with it 🙂 !