to create a new comboBox
when you post your form checkbox_name will contain the selected value
$(document).ready(function() {
var cb = "checkbox_name";
comboBox(document.getElementById(cb+"CB"), cb);
var sel = myForm.elements[cb+"_hold"];
sel.length = 0;
//add options
sel.options[sel.options.length] = new Option("text", "value");
});
<div id="checkbox_name"></div>