You will still have the old MySQL server behaviors available to you to use for older pages.
If you use the standard server behaviors access points, it will generate MySQL code, if you use the access points for the MySQLi server behaviors, it will generate MySQLi code.
The system requirements for the mySQLi server behaviors requires php 5.2 or newer. so if you have a php version older than 5.2, no the mySQLi behaviors will not work.