Problem with CSS and php integration

Here is the page for reference: http://www.londes.com/aa
I have that website I am figuring out right now divided into three seperate pages using PHP, header, data section, and a footer. The drop-down menu's are in the header. The header can be viewed at http://www.londes.com/aa/header.php.

The header page appears to work properly. However, whenever the header loads on any of the main data frames, the drop-down menu's stop working where the main data page starts (try clicking some of the bottom links on one of the pages). I don't really know how to fix this.
Also, the drop down menu uses button's html programming with <li> and what not, which is affected by the CSS programming. However, I also use buttons on the main part of the website, so the CSS screws that up. Is there any easy way to fix that? Can I somehow rename the <li> so it works properly. One of the pages that you can see doesn't work with a bulleted list is: http://londes.com/aa/products/autodiscounts.php.

Thanks, and if you have any advice or questions you can e-mail me at ulrichlondes2@yahoo.com or IM me at 'mlondes'.

I can't reproduce the problem. It works fine on my FF, although the drop-downs are a bit misaligned.

Seeing sub-menus in IE and FF however in IE you cannot get the cursor over all the sub-menu options before the menu closes.

Layou of menus different in FF from IE. In FF they are scrunched up on the right-hand side but the sub-menu opens in the correct position relative to its parent link. In IE, the sub-menu opens displaced vertically up from its parent link.

Layout and operation seem correct in Opera.

W3C validation shows 16 errors so you might like to put these right and see where you go from there.