You fail to tell us what image your having trouble with. I'm guessing it's the images in the pop up's. These images are in a table and the table is in a div. Unless you give a div a width it will take the width of it's parent, in this case the whole page. So using margin:auto; on the tables will center them.
This may bring up a problem with the <p><a href="http://www.designbombs.com/"></a></p> centering when you place text or an image in there, but you should be able to handle that.
I suggest you learn or use a style css section instead of inline. Would make things easier.