Need help with a slide out menu

Okay so I am very new to javascript, but I am trying to make the best of it!

I have one button that I want to have a simple pop out menu on mouseover. I have the pop out menu working as It should but I need some help on getting the pop out to stay visible until the mouse has left either the original button or the pop out.

Here is my code so far, I just need some help on the best way to structure the code to keep this thing open until the mouse leaves the whole area:

<script type="text/javascript">

window.onload = fancybuttons;

	
		
	function fancybuttons() {
		document.getElementById("menu").onmouseover = function(){
			document.getElementById("buymenu").style.display = "block";	
	}
		document.getElementById("menu").onmouseout = function(){
			document.getElementById("buymenu").style.display = "none";	
		}
	
       		
}


</script>

Code (markup):

 

Can anyone help me with this?

Again, I think I just need some direction on divs and such to keep the menu out while the mouse is over both the original button and the actual menu.