function preloadHeaders()
{
    var headers = document.getElementsByTagName("h1");
    for (i = 0; i < headers.length; i++)
    {
        // Grab text
        var headingText = headers[i].firstChild;
        headers[i].removeChild(headingText);
        
        var newImgTag = document.createElement("img");
        newImgTag.setAttribute("src", "/images/header_" + headingText.nodeValue.replace(/ /g, "_") + ".png");
        newImgTag.setAttribute("alt", headingText.nodeValue);
        headers[i].appendChild(newImgTag);
    }
    preloadNav();
}
function preloadNav()
{
    // Wrap each a tag with onMouseOver/onMouseOut
    var links = document.getElementsByTagName("a");
    for (i = 0; i < links.length; i++)
    {
        // grab first child element (img tag)
        var imgTags = links[i].getElementsByTagName("img");
        if (imgTags.length == 0) continue;
        var imgTag = imgTags[0];
        
        // add mouse over events
        imgTag.onmouseover = function(event)
            {
                var el;
                if (navigator.appName == "Microsoft Internet Explorer")
                {
                    el = window.event.srcElement;
                }
                else
                {
                    el = event.target;
                }
                el.src = el.src.replace(/_unselected/, "_selected");
            };
        imgTag.onmouseout = function(event)
            {
                var el;
                if (navigator.appName == "Microsoft Internet Explorer")
                {
                    el = window.event.srcElement;
                }
                else
                {
                    el = event.target;
                }
                el.src = el.src.replace(/_selected/, "_unselected");
            };
        
        // (for performance) preload images
        var tmp = new Image(25, 25);
        tmp.src = imgTag.src.replace(/_unselected/, "_selected");
    }
}