While running Exchange 2003 Deployment Tools (ExDeploy.hta), Step 7 states: Run DomainPrep to prepare the domain for Exchange 2003. To run DomainPrep, your account must have Domain Administrator and local machine administrator permissions.

Specify a path to Domain Prep Setup, from the Exchange deployment check list, click the Browse button to select from the Exchange Server 2003 Installation CD the following setup file in the path: c:\setup\i386\setup.exe

And then click the link below the setup file input box that states:

Run DomainPrep now

Follow the wizard.