Here's a snipet from the .ascx of one of my module's edit control:

<td class="SubHead" align="right" width="20%">Membership Expires:&nbsp;</td>
<td class="NormalBold" align="left" width="30%">
       <asp:textbox id="tbMembershipExpires" tabIndex="23" cssclass="NormalTextBox" columns="20"
             runat="server" MaxLength="20" Enabled="False">
       </asp:textbox>&nbsp;
       <asp:hyperlink id="cmdMembershipExpiresCalendar" tabIndex="-1" cssclass="CommandButton" runat="server">Calendar</asp:hyperlink>
       <asp:comparevalidator id="valMembershipExpires2" cssclass="NormalRed" runat="server" display="Dynamic"
                  controltovalidate="tbMembershipExpires" ErrorMessage="Invalid date" type="Date" operator="DataTypeCheck">
       </asp:comparevalidator>
</td>

And from the corresponding vb codebehind:

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Try

       If Not (Request.QueryString("CenterID") Is Nothing) Then
              CenterID = CInt(Request.QueryString("CenterID"))
       End If
       DotNetNuke.Common.Globals.SetFormFocus(tbCenter)

       cmdMembershipExpiresCalendar.NavigateUrl = CType(DotNetNuke.Common.Utilities.Calendar.InvokePopupCal(tbMembershipExpires), String)

       If Not IsPostback Then

       'other code here

      End If