Most of them use absolute position to put it at the top, and the alignment has a lot to do with the width specified on the div.topnav{} selector in stylemojo.css:
div.topnavwrap { position:absolute; top:0; left:0; margin:0px 0px 0px 0px; width:95%; z-index:100; padding:5px 0px 7px 10px; }
div.topnav { width: 940px; margin-left:auto; margin-right:auto; }
If you adjust the width there you should be able to see changes in the alignment.
Hope that helps,
Joe