JavaScript or browser detection

Hiya, I know it is probably out there somewhere, but I cannot find out a script to detect the browser. I have seen it, and I sorta remember how to do it, but I just can't find it! I have a script that adds nice features to my webpage, but if JavaScript is off the site still can be used. Basically the script does not work in Netscape 4.08 but works above that, so either I could bracket out and check the code, but in this case I cannot as it is code I am not allowed to alter, and I include it, it is not in my HTML file. So I need a way to say in PHP this is a bad web browser for JavaScript, so ignore this bit of the file. Thanks, Steve