Joomla! 1.5 provides a generic Mail-To-Friend component, called ''com_mailto''.  It's very easy to implement.

In your component, you will create a small form and Javascript action:

<code php>
<script language="JavaScript" type="text/javascript">
<!--
function mailToFriend() {
  if (document.mailToFriend) {
    window.open('about:blank',
      'MailToFriend',
      'width=400,height=300,menubar=yes,resizable=yes');
    document.mailToFriend.submit();
  }
}
-->
</script>
<form action="index2.php" name="mailToFriend" method="post" target="MailToFriend" style="display:inline">
  <input type="hidden" name="option" value="com_mailto" />
  <input type="hidden" name="link" value="<?php echo urlencode( JRequest::getURI() );?>" />
</form>

...

<a href="javascript:void mailToFriend()">
  <?php echo JText::_( 'Mail to Friend' );?></a>
</code>

When the link is clicked, it will open a new browser window with the wherein your visitor can enter the details for mailing.  All you need to to is pass a ''link'' field to the form, it does the rest.  A minor degree of CAPTCHA support is given in the popup form.