Setting shmmax in /etc/rc on Mac OS X to install Postgres

Would you please take a look at my problem thoroughly explained in this post on the Macrumors forum?  Any ideas on how to deal with this lack of memory problem?

I posted messages to numerous forums, to Mac and Postres support.  BTW I've been working on this problem, off and on, for 3 months now.

Any advice appreciated.

Thank you, Doug