"Filtering"

Hi!

When I use an `nmap´ scan against some computers I see that some
(most, to be exact) ports have the status `filtered´.

How can I switch the port "status" to filtered my firewall (`iptables´
1.2.9)? Switching to this status I can access the services running in
those ports?

Thanks, sorry by the pooooooooor englihs :P

Max