how to filter IPs that can connect to 1433 ?

Hi,
I have SQL 2005 express running on 2003 server (standard). How do I filter
packets to allow on 2 IP addresses to connect to 1433 ?
My router has a NAT table for port forwarding but I don't have an firewall
rules to filter IP traffic.
Is these a facility on 2003 server or SQL 2005 that would allow me to packet
filter by IP address ?
(guess I could just install ISA server on it but this seems a little
extreme).
Thanks
Scottits ok found the ip security in local policy.