img1 = new Image;
img2 = new Image;

img1.src = 'graphics/glowna/plus.gif';
img2.src = 'graphics/glowna/minus.gif';

function ObsluzPodmenu(ID, img)
{
   e = document.getElementsByTagName('div');
   for (i = 0; i < e.length; i++)
   {
      if (e[i].id.indexOf('r'+ID+'e') > -1)
      {
         styl = e[i].style.display;
         if (styl == 'block')
         {
            e[i].style.display = 'none';
            img = img1;
         } else
         {
            e[i].style.display = 'block';
            img = img2;
         }
      }
   }
}