LinuxQuestions.org - caching only DNS server in RedHat 5

Hello and how r u?I hope u will well and fine .
Last time i had disussed u with cahching DNS server in Linux not forwarding DNS.Actually our organization is very big probably in mornig time 1300 computer run at a time all these computer are connected with internet with single proxy server on which have 5 MB internet link with real ip is 221.120.210.82 and router default gateway is 221.120.210.81 oky which is provided by PTCL.And
two real ip reserve for dns which is 221.120.210.84 us primary and 85 use for secondary DNS server.According to this this senario i want to caching only DNS server so that all the 1300 computers dns request go to our caching dns which authoritative with IANA.

Now or caching dns server have three NIC cards. one fix for real ip like 221.120.210.84 which give as a use for dns from PTCL.

and 2nd NIC which have ip 172.16.0.6 use for as dns for locally our whole the university except out department;and 3rd NIC crad which have ip 172.19.0.17 use for as a dns locally for our department only.

It means whenever user open his internet explorer type any site name
the associtated dns request go to our caching only dns server with ip 172.16.0.6 which is use for rest of whole usniversity not our department similarly whenever our department to this it dns request go to our caching dns with ip 172.19.0.17 this is load balancing with whole uviversity and our department.

tell me how i can make caching only dns server for our university in linux with three nic cards one for real ip others both for local ips.
please send all the procedure step by step kindly .

Remember this caching only server i want to configure in RedHat Linux 5
not 4

Please help me how i can configure caching only dns server with three NIC cards.please explain step by step