Our last client project included a bar chart of active projects with a bar extending from a project's start to end date.  Its very client specific code but it might serve as a good starting place for someone who needed to create a more general gant chart.

The code is uploaded to:
http://openacs.org/storage/file?file_id=93577

Included is a screen shot and the graphic used to create the chart.

The code was written by W. Scott Meeks