A very brief overview of PostgreSQL (and MySQL, too) can be
found on Apple's Development site (
http://developer.apple.com/
internet/macosx/osdb.html).
You may need to register which is free, but you'll prompted to
sign up for pay levels of service.
I guess as an ADC member I should evangelize for OpenACS.
Before I do that I need a volunteer to run through the HOWTO
with Mac OS X.1 on a fresh system. If you are willing to do this
please contact me!
Enjoy,