Dear alan sir,
I can\'t give you a precise command line but I can give you some hints.
first you will need to know what interfaces you have, so run \"ifconfig\" as root, it will list the interfaces by name. I have \"eth0, eth1 and lo\", I think you should get something like ppp0, usbnet? and lo.
next step is to make an iptables rule so use \"man iptables\" and some google searches for NAT-HOWTO, basically something like this (from the NAT-HOWTO):
# Load the NAT module (this pulls in all the others).
modprobe iptable_nat
# In the NAT table (-t nat), Append a rule (-A) after routing
# (POSTROUTING) for all packets going out ppp0 (-o ppp0) which says to
# MASQUERADE the connection (-j MASQUERADE).
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
# Turn on IP forwarding
echo 1 ] /proc/sys/net/ipv4/ip_forward
sounds complex but it really isn\'t, just try a few permutations and you will strike gold soon, if my z arrives soon I will post a better example