how to open a calendar window, select date and close window

I have a region dropdown list and startdate text box on an asp.net 2.0 form. When user click on the image next startdate text box, the calendar window will show and let user select date, then I want date selected to write  back into startdate text box and close calendar window. How to do it? please provide code.

I have partial code.

<asp:TextBox ID="tbStartDate" runat="server"></asp:TextBox><img id="imglStartDate" src="../images/calendar_icon.gif" style="position: relative" alt="Calendar" language="javascript" onclick="return imglStartDate_onclick()" width="20" height="19" />


function imglStartDate_onclick() {
    newwindow=window.open('dateselect.aspx','datewin','height=300,width=300');
      if (window.focus) {newwindow.focus()}

}

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