Create first page : Default.aspx
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<div id="div1" style="position: fixed;right: -240px;width: auto;z-index: 10005;top:235px; right:0px;">
<a href="javascript:var w =window.open('quick-enquiry.aspx',null,'width=300,height=250,location=no,toolbar=no,left=300, top=50,scrollbars=yes')">
<img src="images/enquiry-panel.png" alt="Quick Enquiry" style="border:0px"></a>
</div>
<form id="form1" runat="server">
<div>
</div>
</form>
</body>
</html>
Create Enquiry form : quick-enquiry.aspx
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Enquiry Form</title>
</head>
<body>
<form id="form1" runat="server">
<table cellpadding="0" cellspacing ="0" width="300px">
<tr><td colspan="2"><b>Enquiry Form</b></td>
<tr>
<td>Name : </td><td><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></td></tr>
<tr><td>Email : </td><td><asp:TextBox ID="TextBox2" runat="server"></asp:TextBox></td></tr>
<tr> <td>Contact No : </td><td><asp:TextBox ID="TextBox3" runat="server"></asp:TextBox></td></tr>
<tr><td>Address : </td><td><asp:TextBox ID="TextBox4" runat="server"></asp:TextBox></td></tr>
<tr><td></td><td><asp:Button ID="Button1" runat="server" Text="Submit" /></td></tr>
</table>
</form>
</body>
</html>
Now run Default.aspx and click on image