All existing MySQL 5.0 user accounts have also been created on the MySQL 5.1 server and all new users will automatically receive one database on each server. However, technically the servers run individually, both have their own port (MySQL 5.0: 3306, MySQL 5.1: 3307), their own data directories, their own log files etc. But the user management, all the activities that can be performed through the website, will automatically run on both servers simultanously.
To access both servers, users can use phpMyAdmin which is available on the db4free.net website. Via a radio button, one can select which server to access. To access the 5.1 server through APIs, it's important to specify the port. For PHP, this can be done as follows:
$dbcon = mysql_connect("db4free.org:3307", "user", "password");
or (using the mysqli extension):
$dbcon = new mysqli("db4free.org", "user", "password", 3307);
If the MySQL monitor client is installed, the db4free database on the MySQL 5.1 server can be accessed like this:
shell> mysql -h db4free.org -P 3307 -u [username] -p[password] [database]
Of course, it's also possible to use other client software, like MySQL QueryBrowser.