Event.observe(window, 'load', function() {
  $('hidden_biking').hide();
  $('hidden_hiking').hide();
  $('biking').onclick = bikeDetails; 
  $('hiking').onclick=hikeDetails;
});

function bikeDetails(){
var bikeyValue = $F('biking'); 
if (bikeyValue == "B"){
$('hidden_biking').show()
return true;
}
else {
$('hidden_biking').hide()
return true;
}
}

function hikeDetails(){
var hikeyValue = $F('hiking'); 
if (hikeyValue == "W"){
$('hidden_hiking').show()
return true;
}
else {
$('hidden_hiking').hide()
return true;
}
}