[Aetae]

Как то так(не проверял)

function byClass(el,cl){
  var e = document.getElementsByTagName(el),i = e.length,arr=[];
  while(i--)if(e[i].className==cl)arr.unshift(e[i]);
  return arr
}

var e=byClass('img','highslide'),i=e.length;
var a = document.createElement('a'),l;
a.onclick=function(){return hs.expand(this)}
a.className='highslide';

while(i--){
  a = a.cloneNode(true); a.href = e[i].src; a.id = 'thumb'+i;
  e[i].parentNode.insertBefore(a,e[i]).appendChild(e[i])
}