如何将div的内容居中?

I have a very simple problem, but I can't seem to solve it. I have a table inside a div, which is the main element. Now I have a td tag inside the table with a width and hight set to that of an iphone screen size. Now I basically want to center that table with its td cell within the div tag, so that the 'screen' will be centered in any browser window. How do I do that?I have a very simple problem, but I can't seem