Código Javascript
:
Ver original<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<script>
function verificar_eleccion(obj){
if(obj.id =='eleccion_1'){
document.getElementById("dinero").style.display='block';
}else{
document.getElementById("dinero").style.display='none';
}
}
</script>
</head>
<body>
<p>
<label>
<input type="radio" name="eleccion" value="gratis" id="eleccion_0" onchange="verificar_eleccion(this)" />
Gratis</label>
<br />
<label>
<input type="radio" name="eleccion" value="pagar" id="eleccion_1" onchange="verificar_eleccion(this)" />
Pagar</label>
<br />
<input type="text" name="dinero" id="dinero" style="display:none" />
</p>
</body>
</html>