Image Drop Down Menu

Hi,

I am trying to fingure out how to make image -horizontal drop down menu
with css. I am not able to hide the sub menu. My goal is to be able to
a:hover main menu then it will list the sub menu(s) or if anyone knows
better ways to do this then please help me out. Thank you!
. Here is what I have so far:
#aboutus a {
background-color:#FF9900;
width:150px;
z-index:500px;
width:100px;
}

#aboutus a:hover {
display:list-item;
border-style:groove;
width:100px;
z-index:500px;
position:relative;
}
#aboutus a:hover ul {

width:100px;
z-index:500px;
}
#aboutus ul li li {
width:100px;
z-index:500px;
}
#aboutus ul li li li {
width:100px;
z-index:500px;
}