The guide is written by Gilbert Wong and it's located at http://www.orchardlabs.com/freebsd/. It will likely be included in the standard OpenACS documentation in the near future.

The other issue is that you might have the wrong postgres driver. There are 2 PG drivers floating around - the nspostgres.so driver which is available from AOLserver.com and the postgres.so driver that is available from openacs.org. You want the postgres.so driver, not the nspostgres.so one.

Good luck!