.ust
{
    background-image: url('images/ust.png');
    background-repeat: no-repeat;
    width: 1000px; /* ust genislik */
    height: 30px;   /* ust yukseklik */
}
.orta
{
    background-image: url('images/orta.png');
    background-repeat: repeat-y;
    width: 1000px; /* orta genislik yukseklik vermeye gerek yok  */
    text-align:left;
}
.alt
{
    background-image: url('images/alt.png');
    background-repeat: no-repeat;
    width: 1000px; /* alt genislik */
    height: 30px;  /* alt yukseklik */
}

<div class="ust"></div>
<div class="orta">
içerik
</div>
<div class="alt"></div>