[RoundCube Users] An install problem

I try to install roundcube in windows, but I got an error below: DB Error in F:\webmail\program\include\rcube_db.inc (63): DB Error: extension not found Fatal error: Call to undefined method DB_Error::query() in F:\webmail\program\include\rcube_db.inc on line 124

My environment: windows 2003 IIS 6.0 php-5.1.1 pear-1.4.5 DB-1[1].7.6 MySQL 5.0.13

php.ini include_path=".;C:\php5\pear;c:\php5\includes" extension_dir = "C:\php5\ext" extension=php_mysql.dll

db.inc.php $rcmail_config['db_dsnw'] = 'mysql://roundcube:roundcube@localhost/roundcube'; $rcmail_config['db_dsnr'] = '';

I search all archives in lists.roundcube.net, but I coudn't find a helpful answer. Thanks to anyone response to the subject.