Pass Value From A Textbox To Selectbox?

have a text box which when searched with 3 characters of vendor name will do ajax request and populate the results below the textbox, beside the box are two arrows pointing to a selectbox, when i clcik on the right arrow after the search the vendor name should to added to the select box....similarly after i add required vendor names, I should be able to delete the name from the select box.I have completed the ajax search part of the textbox, and I am stuck with the passing value to the selectbox portion.