function rollover(img, onoff) {
    str = img.firstChild.src
    if (img.firstChild.className == 'imgON') {return}
    if (str == undefined) {return}
    
    if (onoff) { 
        str = str.substring(0,str.length-4) + 'b.gif'
    } else {
        str = str.substring(0,str.length-5) + '.gif'
    }
    img.firstChild.src = str
}