Cathy,
the current CVS version of OpenACS core does not require PG 7.2.x It also works with PG 7.3.x. However not all packages besides the core support PG 7.3.x yet.
Nagita, it appears that you installed from the OpenACS 4.6 tarball. In that case you will have to use PG 7.2.x as Cathy said.
/Bart
