To center a row of blocks, you should use inline-block:
ul.menu { display: block; text-align:center; }
ul.menu li { display: inline-block; }
IE doesn’t understand inline-block, but if you set it inline just for IE, it’ll still behave as an inline-block:
<!--[if lt IE 8]>
ul.menu li { display: inline }
<![endif]-->