This has to be done using CSS.
add class="centered" to the table tag:
<table class="centered" width="1000" height="600" border="0" align="center" cellpadding="0" cellspacing="0">
then add the following CSS:
.centered {
position: absolute;
top: 50%;
left: 50%;
width:1000px;
height: 600px;
margin-left:-500px;
margin-top:-300px;
}