Hello andaak,
Look what closing your #cssmenu before starting your #content can do for you -
Code:
<div id="content">
<div id='cssmenu'>
<ul>
<li class='active '><a href='index.html'><span>Home</span></a></li>
<li class='has-sub '><a href='#'><span>Index</span></a>
<ul>
<li class='has-sub '><a href='#'><span>Micrsooft Office</span></a>
<ul>
<li><a href='\\x.html'><span>T</span></a></li>
<li><a href='\\x.html'><span>E</span></a></li>
<li><a href='\\x.html'><span>O</span></a></li>
<li><a href='\\x'><span>P</span></a></li>
</ul>
</li>
<li class='has-sub '><a href='#'><span>Product 2</span></a>
<ul>
<li><a href='#'><span>Sub Item</span></a></li>
<li><a href='#'><span>Sub Item</span></a></li>
</ul>
</li>
</ul>
</li>
<li><a href='x.html'><span>Tab1</span></a></li>
<li><a href='x.html'><span>Tab2</span></a></li>
<li><a href='x.html'><span>Tab3</span></a></li>
<li><a href='x.html'><span>Tab4</span></a></li>
<li><a href='x.html'><span>Tab5</span></a></li>
</ul>
<!--end cssmenu--></div>
<div id="content"> /*you cannot re-use an id*/
Using some padding to extend the site is fine... I would put it in the CSS though, yes.
I'm not sure what screws up in IE8. That browser does not support your CSS3 rounded corners but that has nothing to do with " or ' . Could you be more specific?