if (document.images){
	
	//prev next navigation

	previouson = new Image();      
	previouson.src = "images/previous_on.gif"; 
	previousoff = new Image();      
	previousoff.src = "images/previous_off.gif";
	
	nexton = new Image();      
	nexton.src = "images/next_on.gif"; 
	nextoff = new Image();      
	nextoff.src = "images/next_off.gif";
	
}

function imgOff(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "off.src");
        }
}

function imgOn(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "on.src");
        }
}