function initPage() {
   
    var inputs = document.getElementsByTagName("input");
    for (var i=0; i<inputs.length; i++)  {
        if (inputs[i].className.indexOf("bt-") != -1 ) {
            inputs[i].onmouseover = function()
            {
               this.src = this.src.replace(".gif", "-hover.gif");
            }
            inputs[i].onmouseout = function()
            {
                this.src = this.src.replace("-hover.gif", ".gif");
            }
        }
    }
}

if (window.addEventListener)
    window.addEventListener("load", initPage, false);
else if (window.attachEvent)
    window.attachEvent("onload", initPage);