shorewall, forwarding net connection

[Seweryn Kokot <skokot@po.opole.pl>]

Inspired by last posts about iptables/firewall I would like to convert from
/etc/init.d/firewall rules to shorewall. I have an external internet
connection (ppp0, dynamic ip) and want to forward that net connection
by eth0 (192.168.0.1) to another computer. Here are the rules 
in /etc/init.d/firewall:
-----
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -t filter -F 
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -I FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
ifconfig ppp0 mtu 1400 
----
How to represent it in shorewall?
Thanks in advance,
Seweryn