Do not use tables for that... use div instead.
OPEN this in header just after <body> tag:
<div style="width:960px;clear:both;margin: 0 auto;">
and CLOSE it in footer just before </body> tag:
Let me know.
Remember that if you have 1024 you need a width which is less than 1024 otherwise page will stretch, because you need extra pixels to show its full width. 960 pixels it is usually enough even for including scrollbars.