Sur ce script je n'arrive pas a centrer les images quelqu'un aurait la solution ?

<!-- DEBUT DU SCRIPT -->
<script language="JavaScript">
/*
SCRIPT EDITE SUR L'EDITEUR JAVASCRIPT
http://www.editeurjavascript.com
*/
var nbimage= 70;
var width;
var height;
var url;
var alte;
function banniere()
{
numimage= Math.round(Math.random()*(nbimage-1)+1);
if (numimage <= 10)
{
gotosite = "";
url = "Images/01.jpg";
alte = "Bannière 1";
}
if (numimage > 10 && numimage <= 20)
{
gotosite = "";
url = "Images/02.jpg";
alte = "Bannière 2";
}
if (numimage > 20 && numimage <= 30)
{
gotosite = "";
url = "Images/03.jpg";
alte = "Bannière 3";
}
if (numimage > 30 && numimage <= 40)
{
gotosite = "";
url = "Images/04.jpg";
alte = "Bannière 4";
}
if (numimage > 40 && numimage <= 50)
{
gotosite = "";
url = "Images/05.jpg";
alte = "Bannière 5";
}
if (numimage > 50 && numimage <= 60)
{
gotosite = "";
url = "Images/06.jpg";
alte = "Bannière 6";
}
if (numimage > 60)
{
gotosite = "";
url = "Images/07.jpg";
alte = "Bannière 7";
}
if(gotosite != "")
{
document.write ('<A HREF="' + gotosite + '">'); }
document.write('<IMG SRC="' + url + '" ALT="' + alte + '" BORDER=0>')
if(gotosite != "")
{
document.write('</A>')
}
}
</script>
<!-- FIN DU SCRIPT -->