Firewall Rule & DHCP

I just Want to allow access to only those computers that was given a IP through the DHCP server. I need to Block forwarding to every fixed IP address.
To summarize. Only ip address leased by DHCP should by forwarded.
Does anybody know how to do it?=
Thank You

see http://forum.mikrotik.com/t/block-static-ip-users-and-allow-dchp-users/29895/1