If you have OpenACS installed, you could try to get the free version of DB Visualizer, a Java-based application that allows to graph db schemas (it supports both PGSQL and Oracle, among other DB's).
Hope this helps,
Then I tried DataArchitect (from thekompany) which did print but does not look as good initially. If you ask it to show the entire 'core' datamodel it doesn't arrange the tables very neatly so you have to spend some moving tables around and grouping them.
This covers part of the kernel - users and some of objects and cr. It was built with dia, which can output png or pdf. There are tools that autogenerate dia from sql schemas, but there's still a lot of manual work to make them pretty.
which program did you use to draw this data model: http://openacs.org/doc/openacs-HEAD/simulation/internals.html ???