I can't check this directly for IE8 but it should work and for IE8+ and other browsers:

<div style="background-image:url('index_htm_files/banner.png');
background-repeat: no-repeat;
/*background-attachment: fixed;*/
background-size: cover;
position: fixed;
top: 0px;
bottom: 0px;
left: 0px;
right: 0px;
background-size: 100%;
background-position: center top;


padding-bottom: 50%;
/*margin: -5%;*/
"></div>
Acorn