Put AjaxControlToolkit.dll in BIN folder and register assembly in page directive of ur aspx page.
<%@ Register Assembly="AjaxControlToolkit"
Namespace="AjaxControlToolkit" TagPrefix="ajaxToolkit" %>
Now in Head section of page add this javascript method
<script type="text/javascript">
function MouseHover()
{
$find("modelPopupExtender1").show();
}
</script>
The complete HTML source of page will look like this
<%@ Page Language="C#" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Assembly="AjaxControlToolkit"
Namespace="AjaxControlToolkit" TagPrefix="ajaxToolkit" %>
<!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>Ajax Model PopUp Extender With MouseOver Example</title>
<link href="StyleSheet.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript">
function MouseHover()
{
$find("modelPopupExtender1").show();
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<ajaxToolkit:ToolkitScriptManager ID="toolKitScriptManager1"
runat="server">
</ajaxToolkit:ToolkitScriptManager>
<p style="background-color: #9999FF; width: 95%;">
Example of using a ModalPopupExtender with with Mouse Over
<br/></p><br/>
Hover over the hyperlink
<asp:HyperLink ID="HyperLink1" runat="server"
onmouseover="MouseHover();"
Font-Underline="True" ForeColor="Blue">
<b>Mouse Over Here to Open PopUp</b>
</asp:HyperLink> to open pop up
<ajaxToolkit:ModalPopupExtender runat="server"
BehaviorID="modelPopupExtender1"
TargetControlID="HyperLink1"
PopupControlID="popUpPanel"
OkControlID="btnOk"
BackgroundCssClass="modalBackground" >
</ajaxToolkit:ModalPopupExtender>
<asp:Panel ID="popUpPanel" runat="server"
CssClass="confirm-dialog">
<div class="inner">
<h2>
Thanks For Visiting This Site</h2>
<div class="base">
<asp:Button ID="btnOk" runat="server" Text="Ok"/>
<asp:LinkButton ID="LinkButton1" runat="server"
CssClass="close"
OnClientClick="$find('modelPopupExtender1').hide(); return false;"/>
</div></div>
</asp:Panel>
</div>
</form>
</body>
</html>