Drop Down Menu Help

Hi, I am having problems with a horizontal drop down menu in my site. If viewed in Firefox the hidden drop down nested list pushes the main content down. Also, I can't seem to center my navigation either. Any help? Thanks!

Here is a link to the site:
http://www.crosst.org/test/index.html

Here is the CSS:

body {
font:normal 62.5% Verdana, Arial, Helvetica, sans-serif;
padding:0px;
margin:0px;
background: #ffe66d url(images/bg.jpg) top repeat-x;
text-align:center;

}

h1 {
margin-top:25px;
padding:0;

}

.clear {
clear:both;
}

#wrapper {
margin:0 auto;
width:800px;
padding:0px;

}

#bgleft {
margin: 0px 0px 0px 0px;
float:left;
width:90px;
height:150px;
background-image:url(images/header_left.jpg);
background-repeat:no-repeat;
background-position:top left;
}

#bgright {
margin: 0px 0px 0px 0px;
float:right;
background-image:url(images/header_right.jpg);
background-repeat:no-repeat;
background-position:top right;
width:90px;
height:150px;

}

#header {
display:block;
height:150px;
width:646px;
background:url(images/header.jpg) top center no-repeat;
margin:27px 0px 0px 0px;
padding:0px;
}

#content {
width: 667px;
padding:0px;
margin:0px auto;
}

/* start navigation */

#center {
width:646px;
margin:0 auto;
}

#navcontain {
width:493px;
height:32;
margin:0 auto;
padding:84px 0px 0px 0px;

}

#nav{

padding:0px 0px 0px 0px;

}

#nav li {
width:79px;
float:left;
}

#nav li:hover ul, #nav li.sfhover ul {
position:relative;
left:auto;
background:#ffffff;
}

#nav li ul {
float:left;
position: relative;
left:-999em;
background:#ffffff;
}

ul li a{
color:#FFFFFF;
display:block;
width:79px;
height:32px;
float:left;
padding:5px 2px 0px 1px;
text-decoration:none;

}
ul li a:hover, ul li a:active {
color:#0000FF;
background:url(images/over.jpg) top center no-repeat;
width:79px;
height:32px;
padding:5px 2px 0px 1px;

}

ul {
font:bold 1.15em Verdana, Arial, Helvetica, sans-serif;
color:#FFFFFF;
list-style-type:none;
}

.bodycopy {
text-align:left;
text-indent: 10px;
}

.contentleft p {

text-align:left;
text-indent: 10px;
}

#contentright p {
text-align:left;
text-indent: 10px;
}

.contentright p {
line-height:.3em;
margin:0px;
padding:0px;
}

#contentright {
background:#ffffff url(images/rc_brcontent.png) bottom left no-repeat;
height:auto;
float:left;
width: 130px;
padding:10px 10px 10px 10px;
margin:150px 0px 0px 0px;
display:block;
}

.rightwrap {
margin-top:1px;
margin-left:20px;
float:left;
background: url(images/biblehead.jpg) top right no-repeat;
width:180px;

}

.contentleft {
height:auto;
background:#FFFFFF url(images/feather.jpg) bottom right no-repeat;
float:left;
width:445px;
margin: 9px 0px 0px 20px;
display:block;
text-align:left;

}
.contentleft p {
text-align:left;
text-indent:10px;
}

.contentleft_head {
padding:0px;
margin:0px;
}

.contentleft_head h1{
text-align:left;
padding:0px 0px 10px 0px;
margin:0px;
font: bold 1.7em Verdana, Arial, Helvetica, sans-serif;
color:#4284c0;

}

.contentleft_head .subhead {
padding:0px;
font:1.4em bold "Times New Roman", Times, serif;
text-align:left;

}

.contentleft_head h1 .hr_top {
border-bottom:1px solid #000000;
width: 200px;
height:5px;
margin-left:200px;
text-align:right;

}

.titles {
padding-top:5px;
font:bold 1.5em Verdana, Arial, Helvetica, sans-serif;
color:#4284c0;
border-bottom:1px solid #ffe66d;
text-align:left;
width: 400px;
}

.roundedcornr_top div {
background: url(images/roundedcornr_tl.png) no-repeat top left;
}
.roundedcornr_top {
background: url(images/roundedcornr_tr.png) no-repeat top right;
}
.roundedcornr_bottom div {
background: url(images/roundedcornr_bl.png) no-repeat bottom left;
}
.roundedcornr_bottom {
background: url(images/roundedcornr_br.png) no-repeat bottom right;
}

.roundedcornr_top div, .roundedcornr_top,
.roundedcornr_bottom div, .roundedcornr_bottom {
width: 100%;
height: 12px;
font-size: 1px;
}
.roundedcornr_content {
margin: 0px 12px;
float:left;

}

.church {
float:left;
background:url(images/church.jpg) top left no-repeat;
width:190px;
height:137px;
margin:0px 10px 0px 0px;

}

.br_corner {
float:right;
text-align:right;
background:url(images/roundedcornr_br.png) bottom right no-repeat;
height:12px;

}

.bl_corner {
float:left;
background:url(images/roundedcornr_bl.png) bottom left no-repeat;
height:12px;
}

.tab_devotion {
height:30px;
width:130px;
background:url(images/tab.png) top center no-repeat;
font:1.6em "Times New Roman", Times, serif;
color:#FFFFFF;
margin:0px;
padding:0px 0px 0px 0px;
text-align:center;
line-height:30px;
}

.tab_botm {
height:160px;
width:130px;
background:url(images/botm.jpg) top center no-repeat;
font:1.3em "Times New Roman", Times, serif;
color:#FFFFFF;
padding:0px 0px 10px 0px;
text-align:center;
line-height:30px;
}

div .tab_search {
background:url(images/tab.png) top center no-repeat;
font:1.6em "Times New Roman", Times, serif;
color:#FFFFFF;
text-align:center;
line-height:30px;
padding:0px 0px 0px 0px;
margin-top:20px;

}

.tab_search p {
line-height:0px;
padding:0px 0px 0px 0px;
margin-top:0px;
}

.tab_search input {
padding-top:0px;
margin-top:10px;
}

#content_top td {
padding:5px 5px 5px 5px;
}