It's located on the OpenACS 4.6 (and HEAD) trees (see http://dev.openacs.org:8000/).
Yes, it works on PostgreSQL (thanks OpenForce!). The forums on openacs.org run on PostgreSQL.
I don't know if it runs with 4.5. My guess would be not without some tweaking.
We migrated the 3.2.5 openacs.org bboards to forums. The migration scripts will be made available. They would be different for 4.5 bboards though, so you should probably start with forums.
BTW, forums depends on notifications.
