I am moving a site from normal php to wordpress and currently they use jquery-selectmenu plugin for their select menus.
I have tried to enqueu the script in wordpress he
I know this is an old question but adding this as it appears high up in Google and may help others.
Most of the jQuery UI components are included with WordPress but are not enqueued by default, you need to enqueue them with this.
wp_enqueue_script( 'jquery-ui-selectmenu' );
There's a helpful list of the included components and the enqueue string at http://jafty.com/blog/tag/how-to-use-jquery-ui-in-wordpress/