哪位大神帮我一下

我用的是VS2008，C#，现在我将数据都放在datagrid中，但有的太长，我不想全部显示，当鼠标移过来的时候我用一个div全部显示。

JS代码： <script language="javascript" type="text/javascript">
function mouseout() {
var div_FullContent = document.getElementById("div_FullContent");
div_FullContent.style.visibility = "hidden";
}

function mousemove(fullContent) {
var div_FullContent = document.getElementById("div_FullContent");
div_FullContent.style.visibility = "visible";
div_FullContent.innerHTML = fullContent;
div_FullContent.style.top = event.clientY + 3 + document.documentElement.scrollTop;
div_FullContent.style.left = event.clientX + 3 +document.documentElement.scrollLeft;
}
</script>

<div id="div_FullContent" class="movediv" style="visibility: hidden"></div>
CSS： .movediv{
border-top:#B5CAE2 1px solid;
border-right:#7A93AC 1px solid;
border-bottom:#698197 1px solid;
border-left:#A7BFD5 1px solid;
font-size:12px;
background:#DBE5F3;
width:250px;
color:#272F3B;

line-height:150%;
PADDING:4px 6px;
position:absolute; z-index:1;
}

C#后台代码lbl_Principal.Attributes.Add("onmouseover", "javascript:this.style.cursor='hand';");
lbl_Principal.Attributes.Add("onmousemove", "javascript:mousemove('" + ls_Principal + "');");
lbl_Principal.Attributes.Add("onmouseout", "javascript:mouseout();");

但是我但不调试的时候总显示document.documentElement.scrollTop，document.documentElement.scrollLeft为0
div到不了合适的地方，谁能告诉我一下啊，急！！！！！！！！！！！！！！！！！！！