Applies a certain stylesheet depending upon which type of browser is used. In this script, a visitor using any version of Netscape thru and including Netscape 4, the stylesheet named "ns.css" will be used. If the visitor uses Internet Explorer, the stylesheet named "ie.css" will be used. If the visitor uses Netscape 6 or greater (which implements many styles differently than NS4 and IE), then the stylesheet "ns6.css" will be used. You need to create the files "ns.css", "ie.css" and "ns6.css" and put them in the root directory of your page.