The problem appears in IE7 also, are you using IE6?
It appears that an HTML has crept into this theme. If you downloaded a new copy of the theme to build the tapc site, and did not change any code, then you might want to check with the theme author and see if it has been fixed, then you can just get another copy of the theme.
The generated HTML shows that the menu DIV is declared twice, and there appears to be an extra unordered list opening (ul). Most browsers probably apply the 10px of top padding for menu twice, which may be why the nav bar is pushed down. The problem should be in a file called header.php in your theme. Without seeing that code it is hard to guess at what to do, but if you know HTML you may be able to fix it.