Joel,
did you patch your copy of OpenACS 4.5 for PostgreSQL 7.3?
Did you know that only the unreleased HEAD of the OpenACS CVS is compatible with PG 7.3.1?
There is a bug in PG 7.3 that cripples complex queries like the query in the OpenACS site-map index. This is fixed in PG 7.3.1. Hence PG 7.3.1 is mandatory for the OpenACS CVS HEAD.
/Bart