put a a width of 615px to your content style properties... and remove width properties to your post-wrapper... and make your content-wrapper width properties to 100%... and make the width properties of your sidebar-wrapper to 30%... remove the padding-right properties to your post-wrapper
this should explain... :) see below...
#wrapper {
background-color:#FFFFFF;
background-image:url(images/header-top.gif);
background-position:center top;
background-repeat:no-repeat;
clear:both;
color:#A5A5A5;
float:left;
padding-top:20px;
width:100%;
}
#content-wrapper {
float:left;
width:100%;
}
#content {
float:left;
padding:0 0 10px 30px;
width:615px;
}
.post-wrapper {
background-image:url(images/post-bg.gif);
background-position:center top;
background-repeat:no-repeat;
float:left;
margin-bottom:0;
margin-left:-20px;
padding-bottom:0;
padding-left:30px;
}
#sidebar-wrapper {
float:right;
width:30%;
}
im not good in explaining... i hope this helps you... good luck... :)