There is a new article up on the OpenXMLDeveloper.org site showing how to build a basic PresentationML file from text entered into a control. It lets you create numerous slides and specify the title and body for each slide. Check it out: http://openxmldeveloper.org/archive/2006/08/01/424.aspx
There have been some similar scripts out there that folks have posted for creating a WordprocessingML document, but this is the first one I've seen for creating PresentationML documents. Very cool.