The quickest fix for the moment would be to have your users change their security settings on IE6.
They go to Tools, Internet Options then the security tab. They can change the security to either v5.5 of IE or they can press the edit button and enter a website to allow the cookies to pass.
For the P3P specs, you have to add very specific information on your website, but I don't know at this point how you would pass that information along with the cookies from the boards?