header width modification in CSS

[gjh42]

To position the background image within #logoWrapper, try something like
background-position: top center;
To position #logoWrapper in the header, try
margin: auto;

#logoWrapper{
    background-image: url(../images/header_bg.jpg);
    background-position: top center;
    background-color: #ffffff;
    height:75px;
    width:750px;
    margin: auto;
    }