//Determine Operating System
system=navigator.appVersion;
if (navigator.appVersion.indexOf("Mac") != -1 ) {
  OS = "Mac";
} else if (navigator.appVersion.indexOf("PowerPC") != -1 ) {
  OS = "Mac";
} else if (navigator.appVersion.indexOf("Win") != -1 ) {
  OS = "Win";
} else if (navigator.appVersion.indexOf("SunOS") != -1 ) {
  OS = "Solaris";
} else {
  OS = "Linux";
}

//Determine Browser Version
bName = navigator.appName;
bVer = parseInt(navigator.appVersion);

document.write("<!-- " + OS + " using " + bName + " v"+bVer + " -->");

if (OS == "Mac" && bName=="Netscape"){
     // your code here
} else if (OS =="Mac" && bName=="Microsoft Internet Explorer"){
     // your code here
} else if (OS =="Win" | OS == "Linux" && bName=="Netscape"){
     // your code here
} else if (OS =="Solaris" && bName=="Netscape"){
     // your code here
} else if (OS =="Win" | OS == "Linux" && bName=="Microsoft Internet Explorer"){
     // your code here
}