Auto Start second postgresql instance MAC OS X

Hi, I'm used to work with PostgreSQL on Windows but now I've moved to OS X
and I'm having problems to create a service to auto start a new server
(instance) of PostgreSQL.
Firstly I used the PostgreSQL installer to create the first server and the
postgres user, then I used initdb to create another server and until this
step, everything turned fine.
After that, I created a folder on StartupItems with StartupParameters and
the other script.
Here are the contents of the two files:

#walkinsense-pgsql

#!/bin/sh

. /etc/rc.common

# Postgres Plus Service script for OS/X

StartService ()
{
ConsoleMessage "Starting Walkinsense PostgreSQL"
su - postgres -c "/Library/PostgreSQL/8.3/bin/pg_ctl -D
/Users/iMac1/Library/Teste/data -l
/Library/Walkinsense/data/pg_log/startup.log -o \"-p 5440\" start"
if [ -e "/Library/Walkinsense/data/postmaster.pid" ]
then
ConsoleMessage "PostgreSQL 8.3 started successfully"
else
ConsoleMessage "PostgreSQL 8.3 did not start in a timely fashion, please see
/Library/Walkinsense/data/pg_log/startup.log for details"
fi
}

StopService()
{
ConsoleMessage "Stopping PostgreSQL 8.3"
su - postgres -c "/Library/PostgreSQL/8.3/bin/pg_ctl stop -m fast -w -D
/Users/iMac1/Library/Teste/data"
}

RestartService ()
{
StopService
sleep 2
StartService
}

RunService "$1"

#SetupParameters

{
Description = "Walkinsense-pgsql";
Provides = ("walkinsense-pgsql");
Requires = ("Resolver");
Preference = "Late";
Messages =
{
start = "Starting Walkinsense PostgreSQL";
stop = "Stopping Walkinsense PostgreSQL";
};
}

I appreciate your help because I'm wasting a lot of time with this and I
think you could help me easily.
Thanks!!

Diogo