Handling LookUp Columns with more than 20 items

<script type="text/javascript">
$(document).ready(function() {
$().SPServices.SPComplexToSimpleDropdown({
columnName: "LookupCol"
});
});
</script>

columnName is the DisplayName of the column in the form

Use the following Lbraries :

jquery-1.7.2.js

jquery.SPServices-0.7.1a.js