Ajax List Management

I need a simple page to do the following: Show a list of a dozen values in a list pull down menu with an add button next to it. Clicking on the add button adds the selected value e.g. Item 6 to a new list without reposting the whole page. The add process should not allow a duplicate item to be added. There would be a remove button that would remove a selected item from the "Items Already Added" list (without reposting the whole page) Visually it would look something like this List Menu Add Btn Items Already Added Remove Btn -> Item 1. Item 4 -> Item 2. Item 1 -> .. -> Item 12 Here 2 items have been added to the list area (4 & 1) The add button would not allow items 4 or 1 to be added again. Items 4 or 1 could be highlighted in the list and removed by clicking on the remove button. Any questions please let me know