upgrade to iptabels from ipchains

[Esteban <eribicic@xxxxxxxxxxxx>]

i used to have this:

$IPCHAINS -N soporte
$IPCHAINS -A FORWARD -s 10.0.0.0/25  -j soporte
$IPCHAINS -A soporte -s 10.0.1.1 -j MASQUERADE
$IPCHAINS -A soporte -j DENY

how can i do this with iptables?
the idea is to use chains for each group.

thanks!