homeon = new Image();
homeon.src = "images/home_on.gif";
homeoff = new Image();
homeoff.src = "images/home_off.gif";

tourson = new Image();
tourson.src = "images/tours_on.gif";
toursoff = new Image();
toursoff.src = "images/tours_off.gif";

photoson = new Image();
photoson.src = "images/photos_on.gif";
photosoff = new Image();
photosoff.src = "images/photos_off.gif";

contacton = new Image();
contacton.src = "images/contact_on.gif";
contactoff = new Image();
contactoff.src = "images/contact_off.gif";

// On function
function imgAct(imgName) {
    document[imgName].src = eval(imgName + "on.src");
}

// Off function
function imgInact(imgName) {
    document[imgName].src = eval(imgName + "off.src");
}