use AJAX Hover Menu Extender as tool tip.
<%-- ADD/REPLACE YOUR AJAX ASSEMBLY HERE --%>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Testing page</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<br />
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br />
<br />
<cc1:HoverMenuExtender ID="HoverMenuExtender1" runat="server" TargetControlID="TextBox1"
PopupControlID="Panel1" PopupPosition="Right">
</cc1:HoverMenuExtender>
<asp:Panel ID="Panel1" runat="server" Style="height: 25px; width: 160px; background-color: #D9D9D9;
border: 1px solid #000000; display: none; text-align: center;">
Enter your first name.
</asp:Panel>
<br />
Move your mouse on text area.
</form>
</body>
</html>