pg_dump error

Hello,

I am getting the following error when trying to use pg_dump:
*******************************************************************
pg_dump cymi > cymi.2000_04_16.dmp
FATAL 1: Memory exhausted in AllocSetAlloc()
PQendcopy: resetting connection
SQL query to dump the contents of Table 'cymi_det_arc_01' did not execute
correctly. After we read all the table contents from the backend,
PQendcopy() failed. Explanation from backend: 'FATAL 1: Memory exhausted
in AllocSetAlloc()
'.
The query was: 'COPY "cymi_det_arc_01" TO stdout;
*******************************************************************

The table it is failing on is about 77MB in size, about 1 million tuples.
The server is dual pentium pro 200, with 512 MB RAM. I'm running PostgreSQL
6.5.2 on RedHat Linux 6.1, 686 SMP kernel. The kernel was recompiled per
Oracle's optimization recommendations for the Linux version of 8i (shared
memory and semaphore parameters, I can list if anyone feels it is relevant).

I tried starting the postmaster with -B10000, -B25000, and -B not there
(i.e. using default buffers). Same error in all three cases.

Any help or suggestions would be appreciated.

Thanks,

Joe