Increasing Max Connections Mac OS 10.3

I installed Postgres 7.4.1 on a dual processor G5 running Mac OS
10.3.2. I'm trying to increase the max_connections to 300 and running
into some trouble. If anyone could shed some light, I'd greatly
appreciate it.

Here's part of my postgresql.conf:

# - Connection Settings -
tcpip_socket = true
max_connections = 300

# - Memory -
shared_buffers = 5000 # min 16, at least max_connections*2,
8KB each
#sort_mem = 1024 # min 64, size in KB
#vacuum_mem = 8192 # min 1024, size in KB

I've tried increasing the shmmax in /etc/rc to a really high number,
but I'm still getting errors when I try to start postgres with pg_ctl:

2004-02-09 11:07:24 FATAL: could not create shared memory segment:
Invalid argument
DETAIL: Failed system call was shmget(key=5432001, size=47030272,
03600).
HINT: This error usually means that PostgreSQL's request for a shared
memory segment exceeded your kernel's SHMMAX parameter. You can either
reduce the request size or reconfigure the kernel with larger SHMMAX.
To reduce the request size (currently 47030272 bytes), reduce
PostgreSQL's shared_buffers parameter (currently 5000) and/or its
max_connections parameter (currently 300).
If the request size is already small, it's possible that it is
less than your kernel's SHMMIN parameter, in which case raising the
request size or reconfiguring SHMMIN is called for.

Here's the relevant part of my etc/rc:

# System tuning
sysctl -w kern.maxvnodes=$(echo $(sysctl -n hw.physmem) '33554432 / 512
* 1024 $
sysctl -w kern.sysv.shmmax=500772160
sysctl -w kern.sysv.shmmin=1
sysctl -w kern.sysv.shmmni=32
sysctl -w kern.sysv.shmseg=8
sysctl -w kern.sysv.shmall=65536

I had previously tried the shmmax settings I'd seen on the forums but
those also gave me an error.