trouble with a join on OS X

I am trying to do fairly simple joins on climate databases that
should return ~ 7 million rows of data. However, I'm getting an error
message on a OS X (10.4 tiger server) machine that seems to imply
that I am running out of memory. The errors are:

psql(15811) malloc: *** vm_allocate(size=8421376) failed (error code=3)
psql(15811) malloc: *** error: can't allocate region
psql(15811) malloc: *** set a breakpoint in szone_error to debug

The query should return all data from all climate stations. In order
to test the query I tried narrowing the SELECT statement to a return
data for a single station. This query worked (ie did not cause the
malloc errors) and returned the expected 200,000 or so rows. Since
this worked I don't think there is a problem with the join syntax.

This a a dual G5 box with 6 gigs of ram running postgresql 8.1. I
have not tired altering kernel resources (as described in http://
www.postgresql.org/docs/8.1/interactive/kernel-resources.html#SHARED-
MEMORY-PARAMETERS), or compiling for 64 bit. I'm just not sure what
to try next. Does anyone have any suggestions?

Best Regards,

Kirk