Confused on implementing popup with javascript

I'd like to understand how this works with Javascript. Basically, I have the popup working with the modal extender in my repeater, (as far as opening and closing the popup with the link in the repeater) and if I can just can the variables of the html dropdown selector and text box to the page I designated in action="alertmod.aspx", I should be able to retrieve them with the request.query method I believe. I changed the button to submit the form to a asp.net button with runat="server", but I think javascript won't require that kind of button running on client side. How do I make the modal extender do what it needs to do to get the data alertmod.aspx? Also, I need to get the TopicID from the sqldatasource and send it along with the other 2 variables. How is this done?

Here what I have currently:

<asp:Repeater ID="forumpost" runat="server" DataSourceID="SqlDataSource1" OnItemDataBound="Forumpost_Onitemdatabound"><ItemTemplate><table border="1" width="99%" align="center"><tr><td align="center"><b>Author</b></td><td><asp:HyperLink ID="HyperLink4" runat="server" NavigateUrl='<%#Eval("TopicID", "replytopost.aspx?tid={0}") %>'>Reply</asp:HyperLink><asp:HyperLink ID="Hyperlink5" CssClass="hideGridColumn" runat="server" NavigateUrl='<%#Eval("TopicID", "editpost.aspx?tid={0}") %>'>Edit</asp:HyperLink><asp:HyperLink ID="HyperLink6" runat="server" NavigateUrl='<%#Eval("Username", "viewposter.aspx?mid={0}") %>'>View Poster Profile</asp:HyperLink><asp:HyperLink ID="BtnShow" runat="server" href="">Alert Moderator</asp:HyperLink><!-- ModalPopupExtender --><cc1:ModalPopupExtender ID="mp1" runat="server" PopupControlID="Panel1" TargetControlID="btnShow"
                            CancelControlID="btnClose" BackgroundCssClass="modalBackground" ></cc1:ModalPopupExtender><asp:Panel ID="Panel1" runat="server" CssClass="modalPopup" align="center" Style="display: none"><h2>
                                Alert Moderators</h2><div id="inline"><form id="contact" name="contact" action="alertmod.aspx" method="post"><label for="alert-type">
                                    Type:</label><select id="alert-type"><option value="0">(Choose an Alert Type)</option><option value="Spam">Spam/Advertising</option></select><br /><br /><label class="reason" for="alert-reason" >
                                    Reason:</label><textarea id="alert-reason" cols="30" rows="5"></textarea></form><br /><asp:Button ID="BtnSubmit" runat="server" Text="Submit" /><div class="float-right error" style="display: none;">
                                    Please fix errors!</div></div><div class="messages" style="display: none;"></div><br /><asp:Button ID="btnClose" runat="server" Text="Close" /></asp:Panel><!-- ModalPopupExtender --></td></tr><tr><td style="vertical-align: top; text-align: center; font-size: large;" width="150px"><asp:Image ID="Avatar1" runat="server" Width="80px" Height="80px" /><br /><asp:Label ID="lbluser" runat="server" Text='<%# Container.DataItem("Username")%>'
                            Font-Size="Large"></asp:Label><br /><asp:Label ID="Lblposts" runat="server" Text="" Font-Size="Small"></asp:Label></td><td width="800px" valign="top"><asp:Literal ID="Literal1" runat="server" Mode="Transform" Text='<%# Container.DataItem("Threadtext")%>'></asp:Literal></td></tr></table></ItemTemplate></asp:Repeater>