The IsRootFolder property evaluates to true if the folder is the root folder, and false otherwise.
<html>
<script language="JScript1.1">
<!--
var myFileSysObj = new ActiveXObject("Scripting.FileSystemObject");
var myFolder = myFileSysObj.GetFolder("\\temp"); if(myFolder.IsRootFolder){
document.write(myFolder.Name + " is the root folder.");
}else{
document.write(myFolder.Name + " is not the root folder.");
}
-->
</script>
</html>