[CSS/HTML] centering in Opera

Okay, so I am in the process of creating an application to view images in (sort of like lightbox) but need to make it cross browser. The biggest issue that I am having is with browsers like Mozilla/FF and Opera; the image is not being centered on the screen, but instead shown in the top right corner.

I am using something like so:

<table style="width: 100%; height: 100%; position: absolute; top: 0; left: 0;">
<td valign="center">
<img src="something.jpg">
Image Number

Which centers the content very nicely in IE 6 (haven’t tested in IE 7 yet) but has no centering in Mozilla/Firefox or Opera.

Does anyone know of a reason that this could be, or how to fix it?