based on your CSS:
#logoWrapper{
background-image: url(../images/header_bg.jpg);
background-repeat: repeat-x;
background-color: #ffffff;
height:75px;
}
you set the height for 75px when the image is clearly larger than 75px.

just a side note I would consider enlarging the width 750px looks too small on wide screen monitors and bigger monitors which almost everyone is using now. I would at least increase the site width to 850px to no more than 980px. Also by having a huge header on all your pages you are taking a way from customer attention.