function toggleOpacity(id, millisec, start, end) { 
    //if an element is invisible, make it visible, else make it invisible
	if(document.getElementById(id).style.opacity == 0) {
		opacity(id, start, end, millisec);
	} else {
		opacity(id, end, start, millisec); 
	} 
}

function opacity(id, opacStart, opacEnd, millisec) { 
    //speed for each frame 
    var speed = Math.round(millisec / 100); 
    var timer = 0; 

    //determine the direction for the blending, if start and end are the same nothing happens 
    if(opacStart > opacEnd) { 
        for(i = opacStart; i >= opacEnd; i--) {
			setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed)); 
            timer++;
			document.getElementById(id).style.visibility = "hidden";
		} 
    } else if(opacStart < opacEnd) { 
        for(i = opacStart; i <= opacEnd; i++) { 
			document.getElementById(id).style.visibility = "visible";
            setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed)); 
            timer++; 
        } 
    } 
} 

//change the opacity for different browsers 
function changeOpac(opacity, id) { 
    var object = document.getElementById(id).style; 
    object.opacity = (opacity / 100); 
    object.MozOpacity = (opacity / 100); 
    object.KhtmlOpacity = (opacity / 100); 
    object.filter = "alpha(opacity=" + opacity + ")"; 
}