in the #sideNavMain li a:visitedselector, you are using a background image.:
#sideNavMain li a:visited { color: #fff; text-decoration: none; font: bold 15px Arial, Helvetica, sans-serif; background: url(../images/misc/orange_bar.png) no-repeat top center;}
IE doesn't like switching between background color and background images. you start off using backgrougnd color for the #sideNavSub li a:link, then switch to using background images.
stick to one or the other, not switching back and forth.