protection for internet in the zte zxdsl 531b

i have 7 computers having wireless card netgear 311 with access point cum router cum modem provided by BSNL having model - ZTE ZXDSL-531B ,i am useing all the computer in network and set the broadband connection in dhcp server and provide all of them WPA-PSK (security) . all of them are working fine . Now the problem is that the internet service is used by all the pc's .and i want that only three pc's can use the internet facality. so, tell how can i do this and all proper setting for the access point & pc's

please........help

thank you