At previous conferences, I showed a utility that could be used to edit the Microsoft Deployment Toolkit wizard XML template files. But as some of you noticed (and e-mailed me about), the utility was nowhere to be found, so I was just teasing you :-)
So I'll tease no more. The Wizard Editor is now available at http://www.codeplex.com/MDTWizardEditor for anyone to download and use. It is provided as-is and could quite easily contain many bugs (for safety's sake, be sure you have a backup copy of the XML file before you change it), so please submit bugs through the CodePlex site; this is done by creating new issues on the "Issues" tab. New feature requests can also be submitted via that mechanism.
If you are interested in contributing to the development of this tool, please let me know. It is officially an open source project, covered by the standard Microsoft Public License terms.