//here you place the ids of every element you want.
var ids=new Array('a1','a2');

function switchid(id){	
  hideallids();
  showdiv(id);
}

function hideallids(){
  //loop through the array and hide each element by id
  for (var i=0;i<ids.length;i++){
    hidediv(ids[i]);
  }		  
}

function hidediv(id) {
  //safe function to hide an element with a specified id
  if (document.getElementById) { // DOM3 = IE5, NS6
    document.getElementById(id).style.display = 'none';
  }
  else {
    if (document.layers) { // Netscape 4
      document.id.display = 'none';
    }
    else { // IE 4
      document.all.id.style.display = 'none';
    }
  }
}

function showdiv(id) {
  //safe function to show an element with a specified id
		  
  if (document.getElementById) { // DOM3 = IE5, NS6
    document.getElementById(id).style.display = 'block';
  }
  else {
    if (document.layers) { // Netscape 4
      document.id.display = 'block';
    }
    else { // IE 4
      document.all.id.style.display = 'block';
    }
  }
}