I think this is what you need if I'm understanding you correctly:
<div id="wrapperHeader">
<div id="header">
<img src="images/logo.png" alt="logo" />
</div>
</div>
div#wrapperHeader {
width:100%;
height;200px; /* height of the background image? */
background:url(images/header.png) repeat-x 0 0;
text-align:center;
}
div#wrapperHeader div#header {
width:1000px;
height:200px;
margin:0 auto;
}
div#wrapperHeader div#header img {
width:; /* the width of the logo image */
height:; /* the height of the logo image */
margin:0 auto;
}