转自：http://blog.csdn.net/yx10/archive/2005/07/18/427766.aspx
效果如下图所示：

  实现原理：

     为DataGrid中的每一行，绑定onmouseover、onmousemove、onmouseout事件，使的鼠标移动到行内时，自动显示一个<div>，鼠标移出该行，就把这个<div>隐藏掉。

实现代码：
     前台：
1．   定义<div>的样式：
<style type="text/css">
.transparent { FILTER: alpha(opacity=85);
BORDER-TOP: indianred 1px solid;
BORDER-RIGHT: indianred 1px solid; 
BORDER-LEFT: indianred 1px solid;
BORDER-BOTTOM: indianred 1px solid;
POSITION: absolute;
BACKGROUND-COLOR: infobackground;
DISPLAY: none  }
</style>
2．   显示和隐藏窗体的脚本：
<script language="javascript">
     //显示弹出窗体
     function Show(Country, City, Address, PostalCode, Phone, Fax)
     {
         document.getElementById("td1").innerText="国家："+Country;
         document.getElementById("td2").innerText="城市："+City;
         document.getElementById("td3").innerText="地址："+Address;
         document.getElementById("td4").innerText="邮政编码："+PostalCode;
         document.getElementById("td5").innerText="电话："+Phone;
         document.getElementById("td6").innerText="传真："+Fax;
         //获得鼠标的X轴的坐标
         x = event.clientX + document.body.scrollLeft;
         //获得鼠标的Y轴的坐标
         y = event.clientY + document.body.scrollTop + 20;
         //显示弹出窗体
         Popup.style.display="block";
         //设置窗体的X,Y轴的坐标
         Popup.style.left = x;
         Popup.style.top = y;
     }
     //隐藏弹出窗体
     function Hide()
     {
         //隐藏窗体
         Popup.style.display="none";
     }
</script>
3．   ToolTip窗体的代码
<div id="Popup" class="transparent" style=" Z-INDEX: 200">
     <table border="0" cellpadding="0" style="FONT-SIZE: x-small">
         <tr>
           <td align="middle" bgcolor="indianred"><font color="white">联系方式</font></td>
         </tr>
         <tr><td id="td1"></td></tr>
         <tr><td id="td2"></td></tr>
         <tr><td id="td3"></td></tr>
         <tr><td id="td4"></td></tr>
         <tr><td id="td5"></td></tr>
         <tr><td id="td6"></td></tr>
     </table>
</div>
后台：
private DataTable dt;
private void Page_Load(object sender, System.EventArgs e)
{
     // Put user code to initialize the page here
     if(!IsPostBack)
     {
          SqlConnection cnn = new SqlConnection();
          cnn.ConnectionString = "data source=localhost;initial           catalog=Northwind;password=;"
         +"persist security info=True;user id=sa;workstation id=APJ062;packet size=4096";
         string sqlstr = "select Top 16 CustomerID, CompanyName, ContactTitle,Country,          City, Address,PostalCode,Phone,Fax from Customers";
         cnn.Open();
         SqlDataAdapter ad = new SqlDataAdapter(sqlstr,cnn);
         dt = new DataTable();
         ad.Fill(dt);
         grdCustomer.DataSource = dt;
         grdCustomer.DataBind();
     }
}
private void grdCustomer_ItemDataBound(object sender,
System.Web.UI.WebControls.DataGridItemEventArgs e)
{
     if(e.Item.ItemType == ListItemType.AlternatingItem
         || e.Item.ItemType == ListItemType.Item)
     {
         e.Item.Attributes.Add("onmouseover",
         "this.oldcolor=this.style.backgroundColor;this.style.backgroundColor='#C8F7FF';");
         e.Item.Attributes.Add("onmousemove",
         "Show('"+dt.Rows[e.Item.ItemIndex]["country"].ToString()+"','"
          +dt.Rows[e.Item.ItemIndex]["City"].ToString()+"','"
          +dt.Rows[e.Item.ItemIndex]["Address"].ToString()+"','"
          +dt.Rows[e.Item.ItemIndex]["PostalCode"].ToString()+"','"
          +dt.Rows[e.Item.ItemIndex]["Phone"].ToString()+"','"
          +dt.Rows[e.Item.ItemIndex]["Fax"].ToString()+"');");
          e.Item.Attributes.Add("onmouseout",
          "this.style.backgroundColor=this.oldcolor;Hide();");
     }
}