IE has a special showModalDialog function that will open a modal window. In the modal window, you must have <base target=_self /> to avoid postback opening another new window. If Coolite is on the modal page, IE6 throws an 'Internet Explorer can not open [page]" error. IE7 works fine.

Parent.aspx
<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Parent.aspx.vb" Inherits="CooliteSandbox.Parent" %>

<!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></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:Button runat="server" Text="Go" OnClientClick="window.showModalDialog('/CooliteSandbox/Child.aspx');return false;" />
    </form>
</body>
</html>
Child.aspx
<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Child.aspx.vb" Inherits="CooliteSandbox.Child" %>

<%@ Register Assembly="Coolite.Ext.Web" Namespace="Coolite.Ext.Web" TagPrefix="ext" %>
<!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">
    <base target="_self" />
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <ext:ScriptManager ID="ScriptManager1" runat="server" Theme="Default">
    </ext:ScriptManager>
    <asp:Label runat="server" ID="lblKey">Hi</asp:Label>
    <asp:Button runat="server" Text="Go" />
    </form>
</body>
</html>
http://blogs.msdn.com/ie/archive/200...n-aborted.aspx