function showPanel(id) {
                var panels = getElementsByClassName('Panel');
                for(var i = 0; i < panels.length; i++) {
                    if(panels[i].id != id) 
                        fadePanel(panels[i].id, true);
                }
                fadePanel(id, false);
            }
            function fadePanel(id, out) {
                if(out) {
                    opacity(id, 100, 0, 500);
                    document.getElementById(id).style.display = 'none';
                }
                else {
                    document.getElementById(id).style.display = 'block';
                    changeOpac(0, id);
                    opacity(id, 0, 100, 500);
                }
            }
            function getElementsByClassName(className, tag, elm){
                var testClass = new RegExp("(^|\\s)" + className + "(\\s|$)");
                var tag = tag || "*";
                var elm = elm || document;
                var elements = (tag == "*" && elm.all)? elm.all : elm.getElementsByTagName(tag);
                var returnElements = [];
                var current;
                var length = elements.length;
                for(var i=0; i<length; i++){
                    current = elements[i];
                    if(testClass.test(current.className)){
                        returnElements.push(current);
                    }
                }
                return returnElements;
            }