Lots of postmaster processes

In our installation of the postgres 7.4.7, we are seeing a lot of the
following postmaster processes (around 50) being spawned by the initial
postmaster process once in a while:

postgres 3977 1 1 Nov03 ? 15:11:38
/s/postgresql-7.4.7/bin/postmaster -D /scratch.1/postgres/condor-db-7.4.7

......

postgres 31985 3977 0 10:08 ? 00:00:00
/s/postgresql-7.4.7/bin/postmaster -D /scratch.1/postgres/condor-db-7.4.7

postgres 31986 3977 0 10:08 ? 00:00:00
/s/postgresql-7.4.7/bin/postmaster -D /scratch.1/postgres/condor-db-7.4.7

postgres 31987 3977 0 10:08 ? 00:00:00
/s/postgresql-7.4.7/bin/postmaster -D /scratch.1/postgres/condor-db-7.4.7

postgres 31988 3977 0 10:08 ? 00:00:00
/s/postgresql-7.4.7/bin/postmaster -D /scratch.1/postgres/condor-db-7.4.7

......

At the same time when these processes being spawned, sometimes there is
also the checkpoint subprocess. I am not sure if that is related. The
document doesn't provide any information. The other activity going on at
the same time is a 'COPY' statement from a client application.

These extra processes put a considerable load on the machine and cause it
to hang up.

Thanks,
Ameet