if (document.images)
{
  <!-- home -->
  but_home = new Image
  but_home_over = new Image
  but_home.src = 'images/home.jpg'
  but_home_over.src = 'images/home_over.jpg'
  <!-- fotos -->
  but_fotos = new Image
  but_fotos_over = new Image
  but_fotos.src = 'images/fotos.jpg'
  but_fotos_over.src = 'images/fotos_over.jpg'
  <!-- videos -->
  but_videos = new Image
  but_videos_over = new Image
  but_videos.src = 'images/videos.jpg'
  but_videos_over.src = 'images/videos_over.jpg'
  <!-- contact -->
  but_contact = new Image
  but_contact_over = new Image
  but_contact.src = 'images/contact.jpg'
  but_contact_over.src = 'images/contact_over.jpg'
  <!-- gastenboek -->
  but_gastenboek = new Image
  but_gastenboek_over = new Image
  but_gastenboek.src = 'images/gastenboek.jpg'
  but_gastenboek_over.src = 'images/gastenboek_over.jpg'
}