window.onload = prepareForms;

function prepareForms() {
  var buttonHover = document.getElementById("butHover");
  buttonHover.onmouseover = function() {
    buttonHover.setAttribute("src", "images/button_CostCoverage_MO.gif");
  }
  buttonHover.onmouseout = function() {
    buttonHover.setAttribute("src", "images/button_CostCoverage.gif");
  }
}