JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" accept-charset="UTF-8" method="post" id="subscribe">
    <div>
        <p>Subscribe to our mailing list, and be among the first to hear about our
            concerts and other events.</p>
        <div id="errors"></div>
        <div class="form-item">
            <label for="name">Your name: <span class="form-required" title="This field is required.">*</span>

            </label>
            <input type="text" maxlength="255" name="name" id="name" size="60" value=""
            class="form-text required" />
        </div>
        <div class="form-item">
            <label for="method">Send me:</label> <span id="method">
                    <label class="inline"><input type="radio" class="radio" name="method" value="E-mail" checked="checked"/> E-mail </label>
                    <label class="inline"><input type="radio" class="radio" name="method" value="Postal Mail"/> Postal Mail </label>
                    <label class="inline"><input type="radio" class="radio" name="method" value="Both"/> Both </label>
                  </span>

        </div>
        <div class="form-item email">
            <label for="email">Your e-mail address: <span class="form-required" title="This field is required.">*</span>

            </label>
            <input type="email" maxlength="255" name="email" id="email" size="60"
            value="" class="form-text required" />
        </div>
        <div class="form-item postal">
            <label for="name">Address: <span class="form-required" title="This field is required.">*</span>

            </label>
            <input type="text" maxlength="255" name="address" id="address" size="60"
            value="" class="form-text" />
            <br/>
            <input type="text" maxlength="255" name="address_2" id="address_2" size="60"
            value="" class="form-text" />
        </div>
        <div class="form-item postal">
            <label for="name">City: <span class="form-required" title="This field is...

CSS

.form-item {
    margin: 1em 0;
}

JavaScript

var postal = $$('.postal'), email = $$('.email'), method;
var setup = function(evt){
  if(evt && evt.element().name == 'method') $('errors').update();
  method = $$('input[name="method"]:checked').first();
  if(method){
    switch($F(method)){
      case 'E-mail':
      postal.invoke('hide').each(function(d){d.select('input').invoke('disable')});
      email.invoke('show').each(function(d){d.select('input').invoke('enable')});
      break;
      case 'Postal Mail':
      postal.invoke('show').each(function(d){d.select('input').invoke('enable')});
      email.invoke('hide').each(function(d){d.select('input').invoke('disable')});
      break;
      default:
      postal.invoke('show').each(function(d){d.select('input').invoke('enable')});
      email.invoke('show').each(function(d){d.select('input').invoke('enable')});
      break;
    }
  }
}
setup();
document.observe('click', setup);