Transferring Selected Options From Multiple Select Box?

I have a multiple select box and want to be able to select from this box and transfer the selection accross to a div using an "Add" button. I have this working fine but I want to append to the list, rather than replace the list when further selections are made.

I somehow need the function to remember the original selected array and then merge the new selected array and the old array if another sleection is made. This is all I have so far...

function editOptions(action)
{
var optionsBox = document.getElementById('optionsBox');
var selectedArray = new Array();

[Code]....