H.323 through a Netfilter (Linux 2.4) firewall

To communicate using a tool like Microsoft NetMeeting or GnomeMeeting through a Linux (kernel 2.4.x-based) firewall, you have to redirect some ports to one IP address in the inside network, otherwise, it won't work. Here is a little script meant to achieve exactly that:
#!/bin/sh
# Script to redirect H.323 trafic to one specific IP behind the firewall

IPTABLES=/sbin/iptables
OUT_DEV=ppp0
IN_HOST=192.168.11.33
TCP_PORT_RANGE=30000:30010
UDP_PORT_RANGE=5000:5003
TCP_LISTENING_PORT=1720

#$IPTABLES -