Problème CSS

Bonjour à tous, j'ai un problème de fichier css. Mon site fonctionne très bien sous firefox, mais sous IE, la disposition est complètement différente.
Voila mon fichier css :

html {
    padding: 0px;
    margin: 0px;
    border: 0px;
}
body {
    margin: 0px;
    padding: 0px;
    border:0px;
    height: 100%;
    width: 100%;
    text-align: center; /* required for centering the page in IE */
    background-repeat:repeat;  /*no-*/
    font-family: Arial, sans-serif;
    font-size: 12px;
    color: #9FF;
    line-height:20px;
    background-attachment:fixed;
    background-position: left bottom;
    background-color:#ffffff;
}

h1, h2, h3, h4, p, ul, li {
    margin: 0px;
    padding: 0px;
    font: 16px Arial,sans-serif;
    line-height:30px;
    list-style-type:none;
}



h1,h2,h3,.componentheading, .contentheading {
    font-family: 'Lucida Sans Unicode', 'Lucida Grande', Arial, sans-serif;
    font-size: 14px;
    font-weight: bold;
    font-style: inherit;
    white-space: nowrap;
    padding-bottom:0px;

    text-align: left;
    color: #FFF;
    width: 100%;

}

h1,.componentheading, .contentheading {

    font-size: 20px;
    padding-top:10px;

    }
    

a:link {
    color: #4fb9f8;
    font-weight: bold;   
}
a:hover {
    text-decoration: none;
}
a:visited{
    font-weight: bold;
}

a.mainlevel:link, a.mainlevel:visited {
    display: block;
    background: url(../images/menu_bg1.png) no-repeat;
    vertical-align: middle;
    font-size: 12px;
    font-weight: bold;
    color: #cff;
    text-align: left;
    padding-top: 5px;
    padding-left: 20px;
    height: 20px !important;
    height: 25px;
    width: 100%;
    text-decoration: none;
}


a.mainlevel:hover {
    background-position: 0px -25px;
    color: #fff;
}

a.mainlevel#active_menu {
    color:#fff;
    font-weight: bold;
}

a.mainlevel#active_menu:hover {
    color: #fff;
}

a.sublevel:link, a.sublevel:visited {
    padding-left: 1px;
    vertical-align: middle;
    font-size: 14px;
    font-weight: bold;
    color: #c64934;
}

a.sublevel:hover {
    color: #900;
}

a.sublevel#active_menu {
    color: #333;
}

.moduletable {
padding-top:10px;

}
.mostread {
list-style-type:none;
}

#wrapper {
    height: 100%;
    width: 990px;
    margin-right: auto;
    margin-left: auto;
    margin-top:10px;
}

#leftwrap {
text-align:left;
width:200px;
float:left;
margin:10px;
float:left;

}

#left{
    width:200px;
    background-image: url(../images/left-mid.png);
    background-repeat: repeat-y;
}

#leftinner2 {
    margin-left:10px;
    margin-right:10px;

}

#right {
    margin-top:10px;
    width:600px;
    float:left;
    text-align:right;
}

#rightinner {
    background-image: url(../images/right-mid.png);
    background-repeat: repeat-y;
    width: 600px;
    margin:0px;
    padding:0px;
    border:0px;
}

#rightinner2 {
    margin-right:20px;
    margin-left:10px;
    list-style-type:none;
    padding: 0px;
    border: 0px;
}

.logoLeft {
    float:left;
    margin:10px;
}

#mainlevel {
    list-style-type: none;text-indent: 0px;
    border:0px;
    padding:0px;
    margin:0px;
}

#mainlevel ul {
    list-style-type: none;
    font-family: Arial, Helvetica, sans-serif;
}

ul#mainlevel a {
    display: block;
    height: 20px;
    padding: 3px;
    position: relative;
    left: 1px;
    width: 192px;
    border-bottom-width: 1px;
    border-bottom-style: solid;
    border-bottom-color: #000;
}

ul#mainlevel a:link,  ul#mainlevel a:visited {
    color: #FFF;
    text-decoration: none;
    font-weight: bold;
}

ul#mainlevel a:hover {
    background-color: #FFF;
    color: #000;
    background-image:none;
}
ul#mainlevel a:link#active_menu, ul#mainlevel a:visited#active_menu {
    background-image:none;
    background-color: #FFF;
    color: #000;
}

li.mostread, li.latestnews{
    padding-bottom:4px;

}

li.mostread, li.latestnews a:link{

    background-repeat: no-repeat;
}

.bear {
float:right;
}
.sublevel {
text-indent:15px;
}

li.contentpaneopen, ul.contentpaneopen {
list-style-type:none;
}

table.contentpaneopen {
width:100%;
margin-left: 5px;
}

.small, .createdate, .modifydate {
line-height:10px;
font-size:90%;
font-style:italic;
padding-bottom:5px;
}

.pagenav3 {
  text-align: center;
  font-size: 11px;
  font-weight: bold;
  border: 3px double #cccccc;
  width: auto;
  background: url(../images/button_bg2.png) repeat;
  padding: 0px 10px;
  line-height: 20px;
  margin: 1px;
  color: #646AF0;
}
table.arbitre {
  background-color:#fdd;
  color:#009;
}

Il doit y avoir une balise css que IE n'aime pas.
Est-ce que quelqu'un pourrait m'aider ? Merci :)

Configuration: Windows XP
Firefox 2.0.0.8