looseUDP

Hi
I have a little network (4 Win98/2k pcs) connected to the internet via an e-smith 4.1server. I want to play Starcraft on one of these computers, so I need to activate the looseUDP patch. A tutorial tells me to edit the rc.firewall file in /etc/rc.d/. But there is no such file. I need to change the line
echo "0" > /proc/sys/net/ipv4/ip_masq_udp_dloose
to
echo "1" > /proc/sys/net/ipv4/ip_masq_udp_dloose

Does anyone know where to find this line? Or maybe another way to activate the patch?
Thanks in advance
CornedBee

P.S. Should I post this in advanced forum?