if (document.images) 
{
      img1 = new Image();
      img2 = new Image();
      img3 = new Image();
      img4 = new Image();
      img5 = new Image();
      img6 = new Image();
      img1.src ="images/link_home_over.gif"; 
      img2.src ="images/link_about_over.gif"; 
      img3.src ="images/link_contact_over.gif";
      img4.src ="images/link_services_over.gif"; 
      img5.src ="images/link_projects_over.gif"; 
      img6.src ="images/link_research_over.gif";
}