if (window.navigator.appName.toLowerCase().indexOf("microsoft") > -1) {
	// IE 用
}
else {
	// IE 以外用
}

<SCRIPT language="javascript" type="text/javascript">

	var dom,bIE;
	var objXMLHttp;

	if ( document.all ) {
		bIE = true;
		dom = new ActiveXObject("Msxml2.DOMDocument.3.0");
		objXMLHttp = new ActiveXObject("Msxml2.XMLHTTP.3.0");
	}
	else {
		bIE = false;
		dom = document.implementation.createDocument("", "", null);
		objXMLHttp = new XMLHttpRequest();
	}

</SCRIPT>