company_on = new Image();
company_on.src = "img/company_dis.gif";
company_off = new Image();
company_off.src = "img/company.gif";

services_on = new Image();
services_on.src = "img/services_dis.gif";
services_off = new Image();
services_off.src = "img/services.gif";

contact_on = new Image();
contact_on.src = "img/contact_dis.gif";
contact_off = new Image();
contact_off.src = "img/contact.gif";

function rollon(image) {
  if (document.images) {
      document[image].src = eval(image + "_on.src");
  }
}

function rolloff(image) {
  if (document.images) {
      document[image].src = eval(image + "_off.src");
 }
}