Forum OpenACS Q&A: Response to ACS/pg is disrupting AOLserver

Here's exactly what has worked for me (I installed acs under its own account, so user is acs in the pool def):

ns_section "ns/db/drivers"
    ns_param    postgres       "nspostgres.so"

    ns_section "ns/db/driver/postgres"
    ns_param   datestyle       "iso"

    ns_section "ns/db/pool/main"
    ns_param   Driver          "postgres"
    ns_param   Connections     4
    ns_param   MaxOpen         1000000000
    ns_param   MaxIdle         1000000000
    ns_param   User            "acs"
    ns_param   Verbose         "On"
    ns_param   LogSQLErrors    "On"
    ns_param   DataSource      "localhost::acs"

...

ns_section "ns/db/pools"
    ns_param   main            "main"
    ns_param   subquery        "subquery"
    ns_param   log             "log"

...

# Database configuration
    ns_section "ns/server/${servername}/db"
    ns_param   pools           "*"  
    ns_param   defaultpool     "main"

You need the pools section as well as the bit that hooks your virtual server to the pools.