This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
If you add a phpinfo() call to a page, one of the things it prints out is a complete list of all the $_SERVER variables that are being set and their values. You should be able to work out from there which one gives you the information you need.