On June 4, I did a session for Microsoft Belgium on Windows Installer Xml during a MSDN evening session. You can read more about MSDN evening sessions in Belgium here.
In this session, I explained the basic concept of Windows Installer packages and by using a number of demos, showed how to create a fully customized Windows installer packages using Windows Installer Xml.
You can download the slide deck here and a zip file containing the demos can be downloaded here.