Code:
<head>
<script language="JavaScript">
   var number = 0;
   function timer() {
      time = setTimeout("randomEvent()",5000);
   }
   function randomEvent() {
      switch(number) {
        case 0:
          alert("Hello");
        break;
        case 1:
          document.bgColor = "#CC0000";
        break;
        case 2:
          window.open("image.html");
        break;
      }
      number++;
      if (number == 3)
        number = 0;
      clearTimeout(time);
      timer();
   }
</script>
</head>

<body onLoad="timer();" bgcolor="#ffffff" text="#000000" link="#0000ff" vlink="#800080" alink="#ff0000">

</body>
-Matt