how to open a popup window

function OpenPopup()
{
        window.open ("http://www.google.com","Google");
}

<asp:button id="Button1" onclick="javascript:OpenPopup();" runat="server" Text="Go"  />

Code Behind..........
....use any button click.......

Page.ClientScript.RegisterClientScriptBlock(GetType(), "JScript1", "window.scroll(0,0);", true);
                lblEmpSelect.Text = "Please select employee in the list.";
                ModalPopupExtender1.Show();
                Panel1.Visible = true;



Code Behind...........




 <asp:UpdatePanel runat="server" ID="Up">
        <ContentTemplate>
            <asp:Button ID="btnLogClose" runat="server" Style="display: none" />
            <cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="btnLogClose"
                PopupControlID="Panel1" CancelControlID="ImageButton3" BackgroundCssClass="modalBackground"
                DropShadow="false" />
            <asp:Panel ID="Panel1" runat="server" Width="550px" Height="100px" Style="display: none"
                CssClass="modalPopup" BackColor="#FFFFFF" BorderColor="Gray" BorderStyle="Solid"
                BorderWidth="5px">
                <table width="100%" cellpadding="1" cellspacing="1">
                    <tr>
                        <td style="padding-right: 5px; width: 100%" align="right">
                            <table width="50%">
                                <tr>
                                    <td style="width: 95%" align="left">
                                    </td>
                                    <td style="width: 5%" align="right">
                                        <asp:ImageButton ImageUrl="~/Images/close.png" ID="ImageButton3" runat="server" />
                                    </td>
                                </tr>
                            </table>
                        </td>
                    </tr>
                    <tr>
                        <td align="center">
                            <b>
                                <asp:Label ID="lblEmpSelect" runat="server" Text="" ForeColor="Red"></asp:Label></b>
                        </td>
                    </tr>
                </table>
            </asp:Panel>
        </ContentTemplate>
    </asp:UpdatePanel>