CSS. who's fault?

Can somebody please help me? This is driving me fucking nuts. So, when designing in CSS, how in the hell do you center align a fixed width div? See here:

So I know that mozilla doesn’t support the CSS text-align:center; for positioning of elements (which is how I’m doing it in IE). But why in the fuck not? How in the fuck else do I get this main div to align in the middle of the page? This is lame. LAME!