Normally, you call the hidedrivetip function during the onmouseout event.
You can actually call the function on any event, and in your case, via onclick.
For instance, you have something like this:
<a href="http://www.yahoo.com" onMouseover="ddrivetip('Visit Yahoo.com')";
If you want the tooltip to hide during button's click, then add an onclick event to the button calling hidedrivetip function:
Hope that makes sense.
<input type="button" value="Hide Tooltip"