How to create a popup login from cmdSelect in gridview

I want to call a frmLogin as popup window after I click cmdSelect from gridview. Then I want to display the UserId automatically at login form after I choose data from gridview.

This is my login form

<div>
            <table border="0" width="100%" style="margin-removed 25px;" cellpadding="4">
                <tr class="nom" style="background-color: #CCCC00">
                    <td class="auto-style1" align="center">Pengesahan Katalaluan Pelajar</td>
                </tr>
                <tr>
                    <td align="center" valign="middle" class="auto-style1">
                        <asp:Label ID="lblIdP" runat="server" Text="Id Pengguna:" Font-Bold="true"></asp:Label>
                     <asp:TextBox ID="txtIdP" runat="server"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td align="center" valign="middle" class="auto-style1">
                        <asp:Label ID="lblKatalaluan" runat="server" Text="Katalaluan:" Font-Bold="true"></asp:Label>
                     <asp:TextBox ID="txtKatalaluan" runat="server"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td align="center" class="auto-style1">
                        <asp:RequiredFieldValidator ID="reqName1" ControlToValidate="txtIdP" ValidationGroup="valLoginGroup"
                            runat="server" ErrorMessage="* Sila isikan Id Pengguna" ForeColor="Red"></asp:RequiredFieldValidator>
                        <asp:RequiredFieldValidator ID="reqPassword" ControlToValidate="txtKatalaluan" ValidationGroup="valLoginGroup"
                            runat="server" ErrorMessage="* Sila isikan katalaluan" ForeColor="Red"></asp:RequiredFieldValidator>
                        <br />
                        <asp:Label ID="lblError" runat="server"></asp:Label><br />
                        <div style="float: right; width: 100%;">
                            <asp:Button ID="btnLogin" runat="server" Style="float: inherit;"
                                Text="Login" TabIndex="3" ValidationGroup="valLoginGroup" value="login" />
                        </div>
                        <br />
                        <asp:LinkButton ID="LinkButton1" runat="server">Tutup</asp:LinkButton>
                    </td>
                </tr>
            </table>
        </div>

And this is my gridview from another form

<%--Table Grid View--%>
        <table class="TableContent" style="width:100%">
            <tr>
                <td valign="top">
                   <asp:gridView id="gvSenaraiP"  CssClass="gridViewTable" autogeneratecolumns="False" allowpaging="True"  Width="100%"  EmptyDataText="Tiada Rekod"
                       OnRowCommand="gvSenaraiP_RowCommand" runat="server" PageSize="20">
                        <FooterStyle CssClass="gridViewFooter" />
                        <HeaderStyle CssClass="gridViewHeader" />
                        <AlternatingRowStyle CssClass="gridViewAlternating" />

                        <Columns> 
                            <asp:BoundField DataField="ROWNUMBER" HeaderText="No." SortExpression="No." HeaderStyle-Width="2%" ></asp:BoundField>
                            <asp:ButtonField DataTextField="SMP01_Nama" CommandName="cmdSelect" HeaderText="Nama Pelajar" meta:resourcekey="ButtonFieldResource1"  HeaderStyle-Width="15%" ></asp:ButtonField>
                            <asp:BoundField DataField="SMP01_NoMatrik" HeaderText="No. Matrik" SortExpression="No. Matrik" HeaderStyle-Width="15%"></asp:BoundField>
                            <asp:BoundField DataField="SKP01_TKhKaunseling" HeaderText="Tarikh" DataFormatString="{0:dd/MM/yyyy}" SortExpression="Tarikh" HeaderStyle-Width="15%"></asp:BoundField>
                        
                        <asp:BoundField DataField="SKP01_KaunselingID" HeaderText="Hidden">
                                <ItemStyle CssClass="hidden" VerticalAlign="Top" />
                                <HeaderStyle CssClass="hidden" />
                                <FooterStyle CssClass="hidden" />
                            </asp:BoundField> 
                        </Columns>

                        <FooterStyle CssClass="gridViewFooter" />
                        <HeaderStyle ForeColor="White" CssClass="gridViewHeader" />
                        <PagerSettings FirstPageText="<<" LastPageText=">>" Mode="NextPreviousFirstLast" NextPageText=">" PreviousPageText="<" />
                    </asp:gridView>
                </td>
            </tr>
        </table>
        <script type="text/javascript">
            function openwindow() {
                window.open("./frmLogin1.aspx", "openwindowname", "width=200,height=200,scrollbars=no,resizable=no,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no,");
            }
            </script>