--container.js--
var delimiter = ",";
var form_name = 'document.elige_campos.';

function MoveOption (MoveFrom, MoveTo, ToDo) {
  var SelectFrom = eval(form_name+MoveFrom);
  var SelectTo = eval(form_name+MoveTo);
  var SelectedIndex = SelectFrom.options.selectedIndex;
  var container;

  if (ToDo=='Add') {
    container=eval(form_name+ToDo+MoveTo);
  }
  if (ToDo=='Remove') {
    container=eval(form_name+ToDo+MoveFrom);
  }

  if (SelectedIndex == -1) {
    alert("Elija un dato para realizar esta operacion.");
  } else {
    for (i=0; i<SelectFrom.options.length; i++) {
      if(SelectFrom.options[i].selected) {
        var name = SelectFrom.options[i].text;
        var ID = SelectFrom.options[i].value;
        SelectFrom.options[i] = null;
                var j=SelectTo.options.length;
        SelectTo.options[j]=new Option (name,ID);
        i=i-1;
        if(ToDo=='Add'||ToDo=='Remove') {
          //container.value=container.value+name+delimiter;
                  container.value=container.value+ID+delimiter;
                  CheckDuplicates('AddFields','RemoveFields');
                  CheckDuplicates('AddListed','RemoveListed');
        }
      }
    }
        }
SelFields=eval(form_name+'selected');
SelList=eval(form_name+'AddListed');
SelFields.value=SelList.value.substring(0,SelList.value.length-1);
}
function CheckDuplicates (AddListContainer, RemoveListContainer) {
        var AddList = eval(form_name+AddListContainer);
        var RemoveList = eval(form_name+RemoveListContainer);
        var TempAddList = AddList.value;
        var TempRemoveList = RemoveList.value;
        if (TempAddList>''&&TempRemoveList>'') {
    TempAddList = TempAddList.substring(0,TempAddList.length-1);
    TempRemoveList = TempRemoveList.substring(0,TempRemoveList.length-1);
    var AddArray = TempAddList.split(delimiter);
    var RemoveArray = TempRemoveList.split(delimiter);
    for (i=0; i<AddArray.length; i++) {
      for (j=0; j<RemoveArray.length; j++) {
        if (AddArray[i]==RemoveArray[j]) {
          AddArray[i]='';
          RemoveArray[j]='';
          break;
        }
      }
    }
    AddList.value='';
    for (i=0; i<AddArray.length; i++) {
      if (AddArray[i]>'') {
                AddList.value = AddList.value + AddArray[i] + delimiter;

      }
    }
    RemoveList.value='';
    for (i=0; i<RemoveArray.length; i++) {
      if (RemoveArray[i]>'') {
        RemoveList.value = RemoveList.value + RemoveArray[i] + delimiter;
      }
   }
        }

        //AddList.value=AddList.value.substring(0,AddList.value.length-1);
        //RemoveList.value=RemoveList.value.substring(0,RemoveList.value.length-1);
}
--html--

<form name="elige_campos" action="?mod=Escuelas&op=list" method="post" class="former">
	<INPUT type=hidden name=AddListed>
	<INPUT type=hidden name=RemoveListed>
	<INPUT type=hidden name=AddFields>
	<INPUT type=hidden name=RemoveFields>
	<input type=hidden name=selected>
	<input type=hidden name="do" value="1">
	<table cellspacing="0" cellpadding="5" border="0" class="browse">

			<tr>
				<td  width="40%" nowrap>
				Lista de Datos disponibles:<br>
					<select multiple size="17" name="Fields" class="browse">
						<option value="clave">Nro. de Clave
						<option value="cue">Nro. de CUE
						<option value="numero">Nro. de Escuela
						<option value="nombre">Nombre (incluye el numero)
						<option value="region">Region
						<option value="localidad">Localidad
						<option value="departamento">Departamento
						<option value="telefono">Telefono
						<option value="director">Director
						<option value="director_dni">DNI del Director
						<option value="domicilio">Domicilio
						<option value="referente">Referente
						<option value="monto">Monto asignado
						<option value="matr_8">Matric. 8vo.
						<option value="matr_9">Matric. 9no.
						<option value="matr_p1">Matric. pol.
						<option value="circuito">Circuito
						</option>

					</select>
				</td>
				<td width="20%" nowrap>
					<p align="center">
						<input onclick="MoveOption('Fields','Listed','Add');" type="button" value="Incluir ->" name="add_list" class="former">
					</p>
					<p align="center">
						<input onclick="MoveOption('Listed','Fields','Remove');" type="button" value="<- Excluir" name="remove_list" class="former">
					</p>

				</td>
				<td valign="top" align="middle" width="40%" nowrap>
				Datos incluidos en el listado:<br>
					<select multiple size="17" name="Listed" class="browse">
					</select>
				</td>
			</tr>
			<tr>

			<td width="100%" colspan="3" nowrap >
			<p align="center">
			<input type="button" name="B30" value="Anterior" onclick="javascript:history.go(-1);" class="former">
			<input  type="submit" name="B31" value="Siguiente" class="former"> <br>
			</p>
			</td>
			</tr>
</table>
</form>