var rollover_path = "img/content/";
var rollover_suffix = "_over";
var rollover_extension = ".png";

function rollover_preload(element)
{
	var img = new Image();
	img.src = rollover_path + element.name + rollover_suffix + rollover_extension;
}

var rules = {
	'img.RolloverableImage' : function(element)
	{	
		// preload the rollover image
		rollover_preload(element);
		
		// onmouse over handler
		element.onmouseover = function()
		{
			this.src = rollover_path + element.name + rollover_suffix + rollover_extension;		
		}
		
		// onmouse out handler
		element.onmouseout = function()
		{
			this.src = rollover_path + element.name + rollover_extension;
		}			
					
	}
};
	
Behaviour.register(rules);