function msover(btn_name){  
    document.images[btn_name].src=document.images[btn_name].src.substring(0, document.images[btn_name].src.length-7) + "on.jpg"
}

function msout(btn_name){
    document.images[btn_name].src=document.images[btn_name].src.substring(0, document.images[btn_name].src.length-6) + "off.jpg"
}

function msovergif(btn_name){  
    document.images[btn_name].src=document.images[btn_name].src.substring(0, document.images[btn_name].src.length-7) + "on.gif"
}

function msoutgif(btn_name){
    document.images[btn_name].src=document.images[btn_name].src.substring(0, document.images[btn_name].src.length-6) + "off.gif"
}