/* ----////// Эффект прозрачности /////------- */      

#banners a img {      
opacity:0.3; -moz-opacity:0.3; filter:alpha(opacity=40);      
}      

#banners a:hover img {      
opacity:1.0; -moz-opacity:1.0; filter:alpha(opacity=100);      
}

<div id="banners">Код баннера</div>