Postgres using more memory than it should

Hi. I have a problem on one of our production servers. A fairly
complicated query is running, and the backend process is using 30 GB of
RAM. The machine only has 32GB, and is understandably swapping like crazy.
My colleague is creating swap files as quickly as it can use them up.

The work_mem setting on this machine is 1000MB, running Postgres 8.3.0.

Here is an excerpt from top:

top - 15:54:17 up 57 days,  6:49,  3 users,  load average: 20.17, 21.29, 16.31
Tasks: 250 total,   2 running, 248 sleeping,   0 stopped,   0 zombie
Cpu(s):  3.1%us,  2.5%sy,  0.0%ni, 15.2%id, 78.7%wa,  0.0%hi,  0.5%si,  0.0%st
Mem:  32961364k total, 32898588k used,    62776k free,    22440k buffers
Swap:  8096344k total,  8096344k used,        0k free,  6056472k cached

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
27192 postgres  18   0 30.6g  22g 1984 R   31 71.7  32:20.09 postgres: flymine production-release-15.0
192.168.128.84(33736)INSERT 
   650 root      10  -5     0    0    0 S    5  0.0  13:56.10 [kswapd2]
  5513 postgres  15   0  130m  19m  364 S    4  0.1   1067:04 postgres: stats collector process
   957 root      10  -5     0    0    0 D    1  0.0   1:39.13 [md2_raid1]
   649 root      10  -5     0    0    0 D    1  0.0  14:14.95 [kswapd1]
28599 root      15   0     0    0    0 D    1  0.0   0:01.25 [pdflush]
   648 root      10  -5     0    0    0 S    0  0.0  15:10.68 [kswapd0]
  2585 root      10  -5     0    0    0 D    0  0.0  67:15.89 [kjournald]

The query that is being run is an INSERT INTO table SELECT a fairly
complex query.

Any ideas why this is going so badly, and what I can do to solve it?

Matthew

--
 First law of computing:  Anything can go wro
 sig: Segmentation fault.  core dumped.