With PostgreSQL, starting with a clean set is very easy, *provided* you do not want to retain your data or you have already backup.
In that case, I would just say:
dropdb <mydbname>
createdb <mydbname>
createlang plpgsql <mydbname>
Restart aolserver, and we are greeted with installation page in browser.
Corresponding instructions on Oracle is there on installation instruction , on Oracle-OpenACS set up page.
