As Joe said, removing the fixed from the first line under
#art-main will keep the background image from stuttering as you scroll, but you will lose the fixed aspect.
The problem is occurring because the image is on a div element instead of the html or body element (IE doesn't like to play nice like the other kiddies with certain things). If you remove from
background: #CCB48F url('/Data/Sites/8/skins/momperfected/images/page.png') fixed;
and place it on
.pagebody instead it will make the background-image to stay fixed and you will no longer have the stutter.