var linkNames = ["index", "people", "activ"];
sel = 0;

function mOver(btn) {

  if (btn != sel) document.getElementById("btn" + btn).src = "images/" + linkNames[btn] + "On.png";
}

function mOut(btn) {

  if (btn != sel) document.getElementById("btn" + btn).src = "images/" + linkNames[btn] + "Off.png";
}

function mClick(btn) {

  window.location = linkNames[btn] + ".html";
}

function update(pageNum) {

  sel = pageNum;
}