From PostgreSQL wiki
PostNuke is a web content management system implemented in PHP.
PostgreSQL support will ship with the upcoming 8.0 release, and any major bugs are considered release blockers. Greg Smith has a project he needs this for and has been fleshing out the port. This bug report shows the current open issues. To give an idea where the likely remaining weak spots are at, re-installation really needs testing. The big open question here is how compatible random PostNuke extensions will be running against a PG database.