The first step will be to port the core over, and that will probably just involve a handful of folks (at least the whole acs_objects framework).
Afterwards, there are tons of modules that need porting, to both ACS Classic and OpenACS (though aD and others are making good progress porting ACS 3.x modules to ACS 4.0).
You could take a look at Sebastian's port of the datamodel to PG, but be warned it is probably going to change considerably. We're considering using PG's inheritance mechanism directly rather than map the inheritance model to a relational scheme as is done in ACS 4.0 Classic (i.e. the Oracle version).
For now - probably "read as much of ACS 4.0 Classic as you can and stay tuned for futher news" is about all you can do. Learning the ACS 4.0 standards and moving your pset 2 solution to 4.0 is a good thing to do - at this point you probably are better schooled in 4.0 than most of us OpenACS types. Sounds like you'll be up-to-speed and ready to help port modules by the time the ACS 4.0 core is ported.
You might want to download the latest Postgres CVS tip, the ongoing PG 7.1 version which will beta before too long, because we're intending to use it as the base for ACS 4.0. It has new features that will make the port considerably easier.
