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++;
        }
    } else if(opacStart < opacEnd) {
        for(i = opacStart; i <= opacEnd; i++)
            {
            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 + ")";
}

function shiftOpacity(id, millisec, menus) {
	var tmpmenu = "";
	for (var i=0; i<menus;i++ )  {
		tmpmenu = "menu"+i;
		if(document.getElementById(tmpmenu).style.opacity == 1) {
	    	document.getElementById(tmpmenu).style.display = "none";
        	opacity(tmpmenu, 100, 0, millisec);
    	}
	}
    //if an element is invisible, make it visible, else make it ivisible
    if(document.getElementById(id).style.opacity == 0) {
	    document.getElementById(id).style.display = "block";
        opacity(id, 0, 100, millisec,1);
    } else {
    	document.getElementById(id).style.display = "none";
        opacity(id, 100, 0, millisec,0);
    }
}