swap storm created by 8.2.3

I'm running:

PostgreSQL 8.2.3 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
3.4.6 20060404 (Red Hat 3.4.6-3)

My memory settings are:

work_mem = 64MB
shared_buffers = 128MB
temp_buffers = 32MB

I ran a query that was "SELECT field, count(*) INTO TEMP temptable" and
it grew to be 10gig (as reported by top) and brought the whole machine
to its knees.  How do I keep this from happening again?