Windows group released an updated set of Domain Rename tools last week -- download here: http://www.microsoft.com/windowsserver2003/downloads/domainrename.mspx. You'll still need to understand and follow the steps for the XDR-FIXUP utility.

Note the required Exchange version information from the website:
Important: The domain rename operation and the use of the domain rename tools is not supported in an Active Directory forest that has any version of Microsoft Exchange Server prior to Exchange Server 2003 SP1 deployed in it.