It seems that Drupal 4.6.2 likes to try to insert an empty string into a database integer.
Here's the postgresql.log entry when adding a new page ...
LOG: statement: INSERT INTO node (title, body, format, uid, type, teaser, status, moderate, promote, sticky, comment, created, changed, nid) VALUES('asdasdasd', 'my page bodwqeqwy', '1', '2', 'page', 'my page bodwqeqwy', '1', '', '1', '', '2', '1122760641', '1122760641', '8')
ERROR: invalid input syntax for integer: ""
It also seems that MySQL permits this behaviour (bad MySQL!) whilst Postgresql doesn't.