Cache control

Hello, I have an web application that checks users rights to specific parts of the apllication at the beginning of each page. However I noticed, with the help of Jason Barnett, that opera caches pages locally and the users rights check fails. The application works fine with Firefox and IE. So I think I need to prevent the pages from beeing cached. How this can be done? I'm totally inexperinced with this stuff. The authentication is a 2 part task. First the username and password are checked and the user is given or denied access. This works ok with every browser. But once inside the user access rights check to differt parts of the application fails because of the Opera cache. Thanks -Will