if (document.images){

aroff = new Image (159, 20);
aroff.src = "images/b_arch.gif";
aron = new Image (159, 20);
aron.src = "images/b_arch_on.gif";

maoff = new Image (159, 20);
maoff.src = "images/b_main.gif";
maon = new Image (159, 20);
maon.src = "images/b_main_on.gif";

oroff = new Image (159, 20);
oroff.src = "images/b_orig.gif";
oron = new Image (159, 20);
oron.src = "images/b_orig_on.gif";

skoff = new Image (159, 20);
skoff.src = "images/b_sket.gif";
skon = new Image (159, 20);
skon.src = "images/b_sket_on.gif";

whoff = new Image (159, 20);
whoff.src = "images/b_what.gif";
whon = new Image (159, 20);
whon.src = "images/b_what_on.gif";

}

function img_act(imgName)
{
   if (document.images){
      imgOn = eval(imgName + "on.src");
      document [imgName].src = imgOn;
   }
}


function img_inact(imgName)
{
   if (document.images){
      imgOff = eval(imgName + "off.src");
      document [imgName].src = imgOff;
   }
}