JFactory/1.5

/*
 
I handle this code as if it is a snippet of a method or function!!
 
First set up some variables/objects
*/
// get the ACL
$acl =& JFactory::getACL();
 
/* get the com_user params */
 
jimport('joomla.application.component.helper'); // include libraries/application/component/helper.php
$usersParams = &JComponentHelper::getParams( 'com_users' ); // load the Params
 
// "generate" a new JUser Object
$user = JFactory::getUser(0); // it's important to set the "0" otherwise your admin user information will be loaded
 
$data = array(); // array for all user settings
 
// get the default usertype
$usertype = $usersParams->get( 'new_usertype' );
if (!$usertype) {
    $usertype = 'Registered';
}
 
// set up the "main" user information
 
$data['name'] = $firstname.' '.$lastname; // add first- and lastname
$data['username'] = $username; // add username
$data['email'] = $email; // add email
$data['gid'] = $acl->get_group_id( '', $usertype, 'ARO' );  // generate the gid from the usertype
 
/* no need to add the usertype, it will be generated automaticaly from the gid */
 
$data['password'] = $password; // set the password
$data['password2'] = $password; // confirm the password
$data['sendEmail'] = 1; // should the user receive system mails?
 
/* Now we can decide, if the user will need an activation */
 
$useractivation = $usersParams->get( 'useractivation' ); // in this example, we load the config-setting
if ($useractivation == 1) { // yeah we want an activation
 
    jimport('joomla.user.helper'); // include libraries/user/helper.php
    $data['block'] = 1; // block the User
    $data['activation'] =JUtility::getHash( JUserHelper::genRandomPassword() ); // set activation hash (don't forget to send an activation email)
 
}
else { // no we need no activation
 
    $data['block'] = 0; // don't block the user
 
}
 
if (!$user->bind($data)) { // now bind the data to the JUser Object, if it not works....
 
    JError::raiseWarning('', JText::_( $user->getError())); // ...raise an Warning
    return false; // if you're in a method/function return false
 
}
 
if (!$user->save()) { // if the user is NOT saved...
 
    JError::raiseWarning('', JText::_( $user->getError())); // ...raise an Warning
    return false; // if you're in a method/function return false
 
}
 
return $user; // else return the new JUser object