Just to summarize ... based on recommendations from Torben, I installed the FreeBSD OpenACS port, which uses 5.3.1 ... based on the aolserver modules that I see installed after using that port (first what I did manually):
aolserver-4.5.0_3
aolserver-nscache-1.5
aolserver-nsopenssl-3.0.b26
aolserver-nspostgres-4.0
aolserver-nssha1-0.1
aolserver-xotcl-1.5.3_5
I had installed everything *except* the xotcl module, so suspect that that was 'the missing link' ... everything else seems to be the same as what I had originally installed ;(
But, now its running with aolserver 4.5.0, postgresql 8.2 and openacs 5.3.1 ...