Alternativt skal du pakke dit layout ind i en div og så centrere den også. Noget i stil med:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "
http://www.w3.org/TR/html4/loose.dtd"><html>
<head>
<title>Centrer billede over site</title>
</head>
<body>
<div style="position:relative;width:770px;margin:0 auto;">
<img src="" style="position:absolute;left:300px;top:100px;" width="200" height="450">
<table width="770" cellpadding="0" cellspacing="0" border="1">
<tr>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
</tr>
<tr>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
</tr>
<tr>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
</tr>
<tr>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
</tr>
<tr>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
<td>lksajkljs klajkljs slajslj alsdalsdasdasdas dsa as das das dasd</td>
</tr>
</table>
</div>
</body>
</html>