need script for redirect based on IP address

[lHassett]

     I'm hoping one or more of you have a script that you could share 
     with us that will redirect users based on IP addresses when they 
     click on a link (button). 
     
     
     Here's the scenario.  We are bringing up a new service of remote 
     web access to our licensed databases.  We have a "databases" 
     button on all library web pages that for off campus users we want 
     to go to a login page for authentication. For on-campus users, 
     including in-library use, we want them to go to the page (on a 
     different server) which directly accesses the databases with no 
     password required.  At this time, the process actually goes on on 
     three different servers:  our main University server that has all 
     the library pages, the authentication server, and the server for 
     the databases.
     
     We'd like this process to be transparent to the user.  All users 
     initially click on the same button, but end up on different 
     pages, depending on where they are coming from (IP address).
     
     All of the servers are unix based.
     
     
     We would very much appreciate anything anyone can share with us.
     
     Thank you very much.
     
     Leslie Hassett
     Reference Librarian, Library Web Editor 
     Loma Linda University
     lhassett at dwebb.llu.edu