title: JQuery CSS select first & last LI form UL list
body: <p>looking for some help please with the JQuery CSS selector.  I want to identify the first and last LI from the main UL list and alter the CSS class.  The first should be 
  <code>class="grid_4 alpha"</code> 
  and the last 
  <code>class="grid_4 omega"</code></p>
  
  <pre><code>&lt;ul&gt;
      &lt;li id="linkcat-2" class="grid_4 this should be alpha"&gt;&lt;h4 class="widgettitle"&gt;Blogroll&lt;/h4&gt;
       &lt;ul class='xoxo blogroll'&gt;
        &lt;li&gt;&lt;a href="http://wordpress.com/"&gt;WordPress.com&lt;/a&gt;&lt;/li&gt;
        &lt;li&gt;&lt;a href="http://wordpress.org/"&gt;WordPress.org&lt;/a&gt;&lt;/li&gt;
       &lt;/ul&gt;
  &lt;/li&gt;
  &lt;li id="linkcat-2" class="grid_4"&gt;&lt;h4 class="widgettitle"&gt;Blogroll&lt;/h4&gt;
   &lt;ul class='xoxo blogroll'&gt;
    &lt;li&gt;&lt;a href="http://wordpress.com/"&gt;WordPress.com&lt;/a&gt;&lt;/li&gt;
    &lt;li&gt;&lt;a href="http://wordpress.org/"&gt;WordPress.org&lt;/a&gt;&lt;/li&gt;
   &lt;/ul&gt;
  &lt;/li&gt;
  &lt;li id="linkcat-2" class="grid_4"&gt;&lt;h4 class="widgettitle"&gt;Blogroll&lt;/h4&gt;
   &lt;ul class='xoxo blogroll'&gt;
    &lt;li&gt;&lt;a href="http://wordpress.com/"&gt;WordPress.com&lt;/a&gt;&lt;/li&gt;
    &lt;li&gt;&lt;a href="http://wordpress.org/"&gt;WordPress.org&lt;/a&gt;&lt;/li&gt;
   &lt;/ul&gt;
  &lt;/li&gt;
  &lt;li id="linkcat-2" class="grid_4 this should be omega"&gt;&lt;h4 class="widgettitle"&gt;Blogroll&lt;/h4&gt;
   &lt;ul class='xoxo blogroll'&gt;
    &lt;li&gt;&lt;a href="http://wordpress.com/"&gt;WordPress.com&lt;/a&gt;&lt;/li&gt;
    &lt;li&gt;&lt;a href="http://wordpress.org/"&gt;WordPress.org&lt;/a&gt;&lt;/li&gt;
   &lt;/ul&gt;
  &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>I just cannot get the right JQuery.css functio to work.</p>
  
  <p>Help much appreciated  - I can add an id to the master ul if requyired</p>