.imageheader {
text-align: center;
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 140px;
margin: auto;
background-image: url("http://www.goldcash.nl/images/backline3.jpg"); background-repeat: repeat-x;
}

#headerimage {
width: 600px;
height: 100px;
margin: auto;
position:absolute;
top:50%;
left:50%; 
}