function Is() {
 var agent = navigator.userAgent.toLowerCase();
 this.pc  = (agent.indexOf("win") != -1);
 if (!(this.ie4 || this.ns5)) {
  isFlat = true;
 }
}

var is = new Is()

if (is.pc)  
  document.write("<link rel='stylesheet' href='/global-pc.css' type='text/css'>");
 else
  document.write("<link rel='stylesheet' href='/global-mac.css' type='text/css'>");