if(obj.attachEvent){
    // IE用
}else{
    // その他ブラウザ用
}

<script type="text/javascript">
window.onload = function() {
    if(oButton1.attachEvent){
        oButton1.attachEvent("onclick", dispMsg1, false);
        oButton1.attachEvent("onclick", dispMsg2, false);
        oButton2.attachEvent("onclick", dispMsg3, false);
    }
}

function dispMsg1() {
    alert("dispMsg1");
}

function dispMsg2() {
    alert("dispMsg2");
}
function dispMsg3() {
    alert(oButton2.attachEvent);
}
</script>

<input type="button" id="oButton1" value="ボタン" />
<input type="button" id="oButton2" value="確認ボタン" />