iptables Question

["A. Johnson Jeba Asir" <johnson ooty tenet res in>]

Hello all,

Please enlighten how to write the below rules using iptables? and also 
point out some HOWTOs for iptables.

# Enable simple IP forwarding and Masquerading for an internal LAN address 
# in the 192.168.0.x
/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -j MASQ -s 192.168.254.0/24 -d 0.0.0.0/0
/sbin/ipchains -A forward -j MASQ -s 192.168.16.0/24 -d 0.0.0.0/0

Thanks in advance

Regards,
A.Johnson