[Wie kann ich meine]Buttons richtig positionieren?

/* Navigation */
#nav_container {
float: left;
width: 202px;
}

#nav_heading {
background-image: url(http://img.webme.com/pic/p/partnernetzwerk/nav_heading_mt2.png);
height: 31px;
margin: 0px;
}

#nav {
padding: 0;
margin: 0;
background-image: url(http://img.webme.com/pic/p/partnernetzwerk/nav_mt2.png);
}

#nav li {
list-style-type: none;
padding: 3px;
padding-left: 15px;
padding-right: 15px;
font-size: 1.2em;
display: block;
}

#nav a {
text-decoration: none;
}
li.nav_element{
background: url(http://img837.imageshack.us/img837/6020/menubutton.png) no-repeat;
}
li.nav_element:hover{
background: url(http://img821.imageshack.us/img821/7972/menubuttonhover.png) no-repeat;
}

#nav_unten {
background-image: url(http://img.webme.com/pic/p/partnernetzwerk/nav_bottom_mt2.png);
height: 0px;
}

#nav_unten span {
display: none;
}

#nav a {

text-decoration: none;
}
li.nav_element{
   margin-left: 35px;
background: url(http://img837.imageshack.us/img837/6020/menubutton.png) no-repeat;
}
li.nav_element:hover{
   margin-left: 35px;
background: url(http://img821.imageshack.us/img821/7972/menubuttonhover.png) no-repeat;
}