your total page divided into 2 parts "main" and "side bar" which inside content list And content list is inside container and container inside containerbg....like below
<div class="containerbg">
<div class="container">
<div id="header">
<div class="content list">
<div id="main">
<div id="sidebar">
so you have to change some size in css file.
search for
.containerbg { background: #FFF url(../images/bg.gif); margin:0 auto; width:1010px; }
.container { background: #FFF; margin:0 auto; width:970px; }
.content { clear:both; float:left; margin-bottom:20px; width:960px; } and make them as
containerbg { background: #FFF url(images/bg.gif); margin:0 auto; width:1090px; }
.container { background: #FFF; margin:0 auto; width:1050px; }
.content { clear:both; float:left; margin-bottom:20px; width:1040px; }
then
search for
.list #main { float:right; padding-top:18px; width:690px; }
you can see .list #main is 690px so your banner is cross the area
so you have to make it as
.list #main { float:right; padding-top:18px; width:728px; }
now your banner fits
but as you make containterbg,.container,.content you have change your home page as well
like i suggest you make .home #main as width 725px
as well item page
so test it on local server..