I received this advice on another thread which fixed up my issue

#logoWrapper{background-image:url(../images/header_bg.jpg);background-repeat:repeat-x;background-color:#fff;height:106px;line-height:106px;}

and change it to this:

#logoWrapper{background-image:url(../images/header_bg.jpg);background-repeat:repeat-x;background-color:#fff;height:106px;line-height:106px;width:850px;margin:auto;}

With the logo I think there is a float: left tag in there somewhere which influences the behaviour of the logo.