Upgrade from 4.6.5 to 4.7b6

I have 4.6.5 running with 2 websites under the /sites directory on s spare server. I use Apache 2.2.0, MySQL 5.0.18, and PHP 4.4.1. I followed the instructions of: http://drupal.org/upgrade/basic-steps-via-GUI without success.

1. Backup
2. Deleted Drupal 4.6.5
3. Installed 4.7b6
4. Updated settings.php with:

$db_url = 'mysql://abc:0123456789@localhost/databaseabc';
$db_prefix = '';

and

$base_url = 'http' . (isset($_SERVER['HTTPS']) ? $_SERVER['HTTPS'] == 'on' ? 's' : '' : '');
$base_url .= '://' .$_SERVER['HTTP_HOST'];
if ($dir = trim(dirname($_SERVER['SCRIPT_NAME']), '\,/')) {
  $base_url .= "/$dir";
}

for tolerant base URL.

When I run the website/update.php, I get the following error message:

Fatal error: Call to undefined function: drupal_bootstrap() in /opt/lampp/htdocs/index.php on line 13

Any suggestion? I must be missing something simple.

Thanks