It sounds like the postgres driver is not getting loaded. You should have something like the following in your logs before you get to the ns_db error:
[24/Apr/2000:18:27:41][8240.1][-main-] Notice: loading: /usr/local/aolserver/bin/postgres.so
[24/Apr/2000:18:27:41][8240.1][-main-] Notice: PostgreSQL loaded.
If not, you need to compile the postgres driver and make sure it is in the bin directory.
