First off, the stylesheet_new.css is part of the problem as it uses tables and zen cart 1.3.x is mostly tableless...
You can try this, but I could not verify it...
Code:
/*wrappers - page or section containers*/
#mainWrapper {
/* background-color: #ffffff; */
text-align: left;
width: 100%;
vertical-align: top;
}
Should match the header size:
Code:
/* the layout for the table which contains the nav bar */
TABLE.headerNavigation {
background-image: url(../images/nav_bg.gif);
background-color: #000000;
border-right: 1px solid #000000;
border-left: 1px solid #000000;
border-bottom: 1px solid #000000;
width: 900px !important;
}
change main wrapper to 900px from 100% and see if that improves things