div#wrapper #rollover { width: 690px; height: 230px; margin:100px auto 0 auto; list-style-type:none; position: relative;}
div#wrapper #rollover .a { position: absolute; left:0; top: 0; height:230px; width:343px; background-image:url(/images/home/home1_a.jpg); } 
div#wrapper #rollover .mouse-on-a { background-image:url(/images/home/home1_b.jpg); } 
div#wrapper #rollover .b { position: absolute; right:0; top: 0; height:230px; width:343px; background-image:url(/images/home/home2_a.jpg); } 
div#wrapper #rollover .mouse-on-b { background-image:url(/images/home/home2_b.jpg); }