if (document.images) {
    Pic1on = new Image();
    Pic1on.src = "images/buttonoff.gif"; 
    Pic1off = new Image();
    Pic1off.src = "images/buttonon.gif";
}
function picon(imja) {
    if (document.images) {
       document[imja].src = eval(imja + "on.src");
}
}
function picoff(imja) {
    if (document.images) {
       document[imja].src = eval(imja + "off.src");
}
}