DataPicker in GridView

Hi,
I am facing a painful problem using DatePicker in DataGrid. The problem is the when I am clicking the date in the popped up calender, the date is getting greyed but the date value is not getting into the datagrid textbox. The code is given below:

<EditItemTemplate>
<Asp:TextBox ID="txtHelpDeskRequestDate" Text='<%# DataBinder.Eval(Container.DataItem, "HelpDeskCallDate" ) %>' runat="server" Width="70px" ReadOnly="false">
</Asp:TextBox>&nbsp;&nbsp;
<a href="javascript:;" onclick="calendarPicker('form1.txtHelpDeskRequestD ate');" title="Pick Date from Calendar"><img src="/cal.gif" width="16" height="16" border="0" alt="Click Here to Pick up the timestamp" align = "left">
</a>
</EditItemTemplate>


The function is like this:
function calendarPicker(strField)
{
window.open('/DatePicker.aspx?field=' + strField,'calendarPopup','width=250,height=190,res izable=yes');
}

Please Help