Adding rules to Webmin -> Linux Firewall

I am trying to install a pptp server that will enable me to VPN into the network and contact the printer and another server hosting software.

I’ve got as far as being able to VPN in, and get into the one server (in this case .x.100) but once connected, I cannot ping the printer (.x.200)

Following a tutorial I have been advised to add the following rules

# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE && iptables-save
# iptables --table nat --append POSTROUTING --out-interface ppp0 -j 
# iptables -I INPUT -s -i ppp0 -j ACCEPT
# iptables --append FORWARD --in-interface eth0 -j ACCEPT

I’ve tried just copying and pasting them, minus the # into a terminal, but they don’t appear in the web interface as accepted.

Can someone please advise where I am going wrong?

Kindest Regards

Alex Nicol