var aHeaders = $$(".headerimg");

if(aHeaders.length > 1) {
  setTimeout('switchHeader(0)',5000);
}

function switchHeader(iCurrent) {
  iNext = iCurrent+1;

  if(iNext >= aHeaders.length) {
    iNext = 0;
  }

  new Effect.Parallel([oFade   = new Effect.Fade(aHeaders[iCurrent], {sync:true}),
                       oAppear = new Effect.Appear(aHeaders[iNext], {sync:true})], {
                       duration: 1,
                       afterFinish: function() {setTimeout('switchHeader('+(iNext)+')',5000);}
                     });

}