var t=0;

function opacity(id, opacStart, opacEnd, millisec, framerate)
{
    opacRec(id, opacStart, opacEnd, millisec, framerate, 1);
}

function opacRec(id, opacStart, opacEnd, millisec, framerate, i)
{
    var totalFrames = framerate*(millisec/1000);
    var millisecPerFrame = 1000/framerate;
    var opacChangePerFrame = (opacEnd - opacStart) / totalFrames;

    changeOpac(opacStart+i*opacChangePerFrame, id);

    if (i < totalFrames)
    {
      t = setTimeout("opacRec('" + id + "', " + opacStart + ", " + opacEnd + ", " + millisec + ", " + framerate + ", " + (i+1) + ");",millisecPerFrame);
    }
}

//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 + ")";
    if (opacity == 0) object.visibility = "hidden";
}