si ... cerca in giro...
cmq il succo è la seguente sub da associare
alla selezione del calendario
codice:
     Public Sub ShowDate(ByVal sender As Object, ByVal e As EventArgs)
        Response.Write("<SCRIPT language=""Javascript""><!--" & vbCrLf)

        Response.Write("window.opener." & Request("campo") & ".value='")
        Response.Write(cal.SelectedDate.ToString("dd/MM/yyyy") & "';" & vbCrLf)

        Response.Write("self.close();" & vbCrLf)
        Response.Write("--></SCRIP")
        Response.Write("T>")

    End Sub