Pull Down Menu

I am trying to create a basic pull down menu but somehow I can not make it work.

My basic code is that:

HTML Code:

---

<div id="menu_parent">Main Menu</div>

<div id="menu_child">
<a href="#">Item 1</a>
<a href="#">Item 2</a>
<a href="#">Item 3</a>
</div>

<script type="text/javascript">
at_attach("menu_parent", "menu_child", "hover", "y", "pointer");
</script>

---

but somehow it comes as like that on my page:

Main Menu

Item 1 Item 2 Item 3

Whereas I was supposed to see Item1,2,3 when I put the mouse on the Main Menu.

I saved my file as html and used notepad as editor.

Any help will be great.

Thanks.:)