Hola, como te va?
Mira sobre tu problema, no me base en tu código, sino que busque la funcionalidad:
Cita: <HTML>
<HEAD>
<TITLE>Move Multiple Selections Demo</TITLE><script language="javascript">
function MyMoveItem(fromObj, toObj)
{
for (var selIndex = fromObj.length - 1; selIndex >= 0; selIndex--)
{
// Is this option selected?
if (fromObj.options[selIndex].selected)
{
// Get the text and value for this option.
var newText = fromObj.options[selIndex].text;
var newValue = fromObj.options[selIndex].value;
// Create a new option, and add to the other select box.
var newOption = new Option(newText, newValue)
toObj[toObj.length] = newOption;
// Delete the option in the first select box.
fromObj[selIndex] = null;
}
}
}
</SCRIPT>
</HEAD>
<BODY>
<SELECT ID="possible" NAME="possible" SIZE"10" MULTIPLE>
<OPTION VALUE="New Red Corvette">New Red Corvette</OPTION>
<OPTION VALUE="Vintage Red Corvette">Vintage Red Corvette</OPTION>
<OPTION VALUE="Old Red Corvette">Old Red Corvette</OPTION>
</SELECT>
<SELECT NAME="wishlist" ID="wishlist" SIZE="10" MULTIPLE>
<OPTION VALUE="Old Red Jalopy">Old Red Jalopy</OPTION>
</SELECT><INPUT TYPE="BUTTON" VALUE="Add to wishlist"
ONCLICK="MyMoveItem(possible,wishlist);">
<INPUT TYPE="BUTTON" VALUE="Remove from wishlist"
ONCLICK="MyMoveItem(wishlist,possible);">
</BODY>
</HTML>
Quizas no sea Justo lo que buscas, pero por ahi si lo modificas un poco va.
Saludos!