<script language=javascript>


            var leaktest = 1;


            var leakurl = "http://www.radiozet.pl/radiozet.pls";

            var winampx;
            var hwndset = 0;
            var autoscroll = 1;
            var gecko =  !(navigator.appName == 'Microsoft Internet Explorer');
            var initted = 0;
            ...

leakurl = document.getElementById("select").value;
leakurl = document.URL;

  <select size="1" name="D1">
  <option value="http://www.radiostacja.pl/radiostacja.pls">http://www.radiostacja.pl/radiostacja.pls</option>
  <option value="http://www.radiozet.pl/radiozet.pls">http://www.radiozet.pl/radiozet.pls</option>
  </select>

<script language=javascript>

            var leaktest = 1;
            var leakurl = document.getElementById("D1").value;