Help please….menu dropdown position???

So, I have finally worked out how to center my navigation menu horizontally in a cross-browser compatible way. The problem I now have though is with my dropdowns. They have inherited some of the attributes I used to center the nav and now, when the menu parent page is hovered over, the dropdown pops up over it, rather than under and to the side a bit. I’ve tried a few fixes though am not sure the best way to go about resolving the issue in the most browser friendly way. Do I need a different position attribute or alignment or something? I can’t get margin or padding to work.
Here’s the code:

#nav {
	-khtml-border-radius: 0px;
	-moz-border-radius: 0px;
	-webkit-border-radius: 0px;
	background-image:url(/wp-content/themes/child/images/banner.png);
	border-radius: 0px;
	clear: both;
	color: #555;
	margin: 0 auto 0px;
	overflow: hidden;
	text-align: center;
	text-transform: uppercase;
	height: 35px;
	width: 920px;
}

#nav ul {
	width: 100%;
	margin: 0 auto;
	display: inline-block;
	list-style: none;
}

#nav li {
	display: inline-block;
	list-style: none;
}

#nav li a {
	color: #90877C;
	display: block;
	font-size: 12px;
	float: left;
	margin: 0px 0px 0px 0px;
	padding: 8px 15px 0px 15px;
	text-decoration: none;
}

#nav li a:hover,
#nav li a:active,
#nav li:hover a,
#nav .current_page_item a,
#nav .current-cat a,
#nav .current-menu-item a {
	color: #90877C;
}

#nav li a:hover {
	color: #222;
}

#nav li li a,
#nav li li a:link,
#nav li li a:visited {
	background: #fbf7eb;
	border-top-width: 0px;
	color: #555;
	padding: 10px;
	font-size: 11px;
	position: relative;
	margin: 0px 0px 0px 5px;
	text-transform: none;
	text-align: left;
	width: 100px;
}

#nav li li a:hover,
#nav li li a:active {
	color: #222;
}

#nav li ul {
	height: auto;
	left: -9999px;
	margin: 0 0 0 -1px;
	position: absolute;
	width: 150px;
	z-index: 9999;
}

#nav li ul a {
	width: 130px;
}

#nav li ul ul {
	margin: -33px 0 0 122px;
}

#nav li:hover>ul,
#nav li.sfHover ul {
	left: auto;
}

Help please…..
??