Almost... I tried:
.poster {
float: none;
background-image: url(../../images/theme/bg_poster.png);
background-repeat: no-repeat;
}
.postarea {
display: table-cell;
width: 100%;
}
div.windowbg, div.windowbg2 {
overflow: auto;
padding: 10px 0;
}
...because I don't want the background to be repeated.