var showed = "p1";
 function zobraz(paragraf)
 {
   if (document.getElementById)
   {
     switch(paragraf)
      {
       case'p1':
         document.getElementById('tp1').className='z2';
         document.getElementById('tp2').className='z1';
         document.getElementById('tp3').className='z1';
         break;
       case'p2':
         document.getElementById('tp1').className='z1';
         document.getElementById('tp2').className='z2';
         document.getElementById('tp3').className='z1';
         break
       case'p3':
         document.getElementById('tp1').className='z1';
         document.getElementById('tp2').className='z1';
         document.getElementById('tp3').className='z2';
         break
      }
   }
   if (document.getElementById)
   {
     document.getElementById(showed).style.display = "none";
     document.getElementById(paragraf).style.display = "block";
     showed = paragraf;
     return false;
   }
   else
   {
     return true;
   } 
 }