why I can't call garland_theme() in template.php for drupal6.5

template.php
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.
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////////////////drupal6.5///////////////////////
function garland_theme() {
print_r( 'test word' ); // not work why ? so user_login_block not work too.
return array(
'user_login_block' => array(
'template' => 'user_login',
'arguments' => array('form' => NULL),
),
// other theme registration code...
);
}

function garland_preprocess_user_login_block(&$variables) {
$variables['intro_text'] = t('This is my awesome login form');
$variables['rendered'] = drupal_render($variables['form']);
}