insufficient file descriptors on Mac OS X

I am trying to start the server (8.2.3 on Mac OS X 10.4.10 (8R2218)
Kernel-Version:Darwin 8.10.1).

I have 3Gb Ram available.

My memory settings are:

Maximilian-Tyrtanias-Computer-2:~ maximiliantyrtania$ sysctl -a | grep shm
kern.exec: unknown type returned
kern.sysv.shmmax: 134217728
kern.sysv.shmmin: 1
kern.sysv.shmmni: 1024
kern.sysv.shmseg: 32
kern.sysv.shmall: 32768

In postgresql.conf:
.
.
.
max_connections = 240
.
.
shared_buffers = 4MB

All other values are still on their defaults.

But, alas...

Maximilian-Tyrtanias-Computer-2:/Users/maximiliantyrtania postgres$
/usr/local/bin/postgres -D /usr/local/pgsql/data/
<%2007-11-09 14:46:42 CETFATAL: 53000: insufficient file descriptors
available to start server process
<%2007-11-09 14:46:42 CETDETAIL: System allows 6, we need at least 20.
<%2007-11-09 14:46:42 CETLOCATION: set_max_safe_fds, fd.c:432

I sure there is some additional setting I have to adjust, but i'm not sure
which one.

Any pointers?

Maximilian Tyrtania