Mira: en tu HTML ponlo así:
Cita: <div id="middle_right">
<div id="middle_left">
<div id="middle_center"> fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
fsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsd ffsdf sdfsdfsd fsd fsdf sdf sdfsdf sdf sdfsdf sdf dsf dsfdsf dsfsdfdsfsdfsd fs dfsdf sd fsdfs dfdsf sdfsd<br />
</div>
</div>
</div>
y en la CSS cambia esto y ponlo así:
Cita: #main #right #middle_left{
position:relative;
background: url(../img/content/middle_left.gif) repeat-y;
margin-right: 7px;
}
#main #right #middle_center{
position:relative;
width:771px;
margin-left: 7px;
}
#main #right #middle_right{
position:relative;
background: url(../img/content/middle_right.gif) repeat-y right top;
}
#main #right #bottom_center{
position:relative;
float:left;
background: url(../img/content/bottom_center.gif) repeat-x left;
height:7px;
width: 771px;
}