Well I can't see on your web-site which image you are referring to, so I'm just going to give a series of general answers.
If you want the image to be centred on the page, do this:
position:absolute;left:50%;left-marginminus half the image width);
That will centre it on any screen but not necessarily centre it in the table (unless your table is also centred). If you want, you could put the image as the first thing in the table and do something like this:
<img src="lavalamp.png" style="position:absolute;left:50%;margintop margin) (right margin) (bottom margin) (left margin);">
you can change the margins to position the image pixel perfect on the page and it will look the same in all browsers and on all resolutions.
Hope this helps but I can't do more without seeing an exmple page of what you're trying.