iptables rules from freeradius...

Hi: i am using freeradius as wireless authenticator. windows xp client is using wpa + peap. and authentication through wireless ap is ok. now i want to setup some iptables rules for authenticated users. i wonder if this can be done via freeradius. can i find out the mac address or ip address information for authenticated users? can i run iptables scripts when a user authenticated successfully ? since ip address is offered by dhcp server after authenticated, i think it's difficult to get this info from freeradius. maybe there are better ways to implement what i want? thanks for reply !!! Best Regards, tbsky