function compatibleIE8(){
var browser = navigator.appName;
var b_version = navigator.appVersion;
if(browser == "Microsoft Internet Explorer"){
var version = b_version.split(";")[1].replace(/[ ]/g,"");
if(version == "MSIE8.0"){
　　.........
}
}
}

2.

1. function isIE() { //ie?  
2.     if (!!window.ActiveXObject || "ActiveXObject" in window)  
3.         return true;  
4.     else  
5.         return false;  
6. }