To move items [options] from one dropdown box[select box] to another is pretty simple.

 
    //This is the function called to 
    //move items from one select box to another
    function moveIt(moveFrom,moveTo)
    {
        var oMoveFrom = 
                      document.getElementById(moveFrom);
        var oMoveTo = 
                      document.getElementById(moveTo);
        addIt(oMoveFrom,oMoveTo);
        removeIt(oMoveFrom);
    }
    //This is the function that 
    //adds it from the "oMoveFrom" to the "oMoveTo"
    function addIt(oMoveFrom,oMoveTo)
    {
      //loop though all elements
      for (var i=0; i < oMoveFrom.length;i++)
      {
           if (oMoveFrom[i].selected)
           {
           //Create new OPTION element and set the new values
            oNewOption = document.createElement("OPTION");
            oNewOption.value = oMoveFrom[i].value;
            oNewOption.text = oMoveFrom[i].text;
            //Add oNewOption to oMoveTo
            oMoveTo.add(oNewOption,oMoveTo.length);
           }  
      }
    }
     //This is the recursive function that 
     //removes it from the "oMoveFrom"
    function removeIt(oMoveFrom)
    {
    //loop though all elements
      for (var i=0; i < oMoveFrom.length;i++)
      {
           if (oMoveFrom[i].selected)
           {
            //Remove it from oMoveFrom
            oMoveFrom.remove(i);
            removeIt(oMoveFrom); //recursive funtion;
            break;
           }  
      } 
    }

 
onclick="moveIt('sltBox1','sltBox2');"