[squid-users] Problem between private network and Public network

I have a problem in my network and proxy server..
The situation is like this.
I have 1 router with 2 NIC (one private and it's NAT to public IP)..then
after router is my squid proxy server(using Public IP). My problem is i
can control public IP access control list (certain public user can
access internet and some cannot)
but i CANNOT control private IP access control list..how to make squid
proxy server possible to take care or to control access of private IP
user??
Please help me, i'm newbie.

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 Yuzz                      
 System Engineer           
 System Integration        
 EmasOnline Dot Com Sdn Bhd
 http://www.EmasOnline.com 
 phone: 606+ 3345666 ext 2104
 fax: 606+ 3372233           
 email: yuzz@emasonline.com