How to get horizontal scroll bar in select box in IE?

I’m not really sure what you’re trying to achieve. This is simply a select list. Just remove your styling and it will automatically size to your contents.

EDIT

Make the container that contains the list scroll. Note: the usability of this is somewhat questionable so I would look for another solution prior to implementing something like this on a page.

<div id="selector_cat"> 
    <select name="sets">
        <option value="general">happy holiday</option>
        <option value="garden">Garden</option>
        <option value="Lunch">Lunch</option>
        <option value="nice day">A nice day out with my friend on the beach</option>
    </select>
</div>

#selector_cat{
    width: 100px; 
    overflow: auto;
}