Using calendar_date_select with Rails 3

Question

I've been trying to create a user date-of-birth selection field during sign up. The code looks like this:

<div id="content">
<h3>Register</h3>  
  <%= form_for(@user) do |f| %>
    <div style="width: 374px; margin: 0 auto;">
      <%= f.label :name %>
      <%= f.text_field :name %>
      <div style="clear: both;"></div>
      <%= f.label :email %>
      <%= f.text_field :email %>
      <div style="clear: both;"></div>
      <%= f.label :dob %>
      <%= f.calendar_date_select "e_date" %>
    </div>
  <% end %>
</div>

When I try to load it, rails gives me this error:

undefined method `calendar_date_select' for #<#<Class:0x00000101210208>:0x0000010120d0a8>

What am I doing wrong?

EDIT I installed the calendar_date_select gem using: gem install calendar_date_select I'm running OS X Snow Leopard if it matters.