function preloadImages() {
    if (!document.images)
        return;
        
    document.preloaded = new Array();
    preloadImage ('about');
    preloadImage ('advantage');
    preloadImage ('careers');
    preloadImage ('contact');
}

function preloadImage (imageName) {
    var img;
    
    img = new Image;
    img.src = 'images/btn-' + imageName + '-active.gif';
    document.preloaded.push (img);

    img = new Image;
    img.src = 'images/btn-' + imageName + '-inactive.gif';
    document.preloaded.push (img);
}

function setImage (imgObject, isActive, sectionName) {
    imgObject.src = 'images/btn-' + sectionName + '-' + (isActive ? 'active' : 'inactive') + '.gif';
}