var ImageRolloverRules = {
	"img.hover-over" : function(el) {		
		el.onmouseover = function(ev) {
			el.src = el.src.substring(0, el.src.length - 6) + 'ov.gif';						
		},
		el.onmouseout = function(ev) {			
			el.src = el.src.substring(0, el.src.length - 6) + 'up.gif';					
		}
	}
}

Behaviour.register(ImageRolloverRules)