It depends on what runs cron on your system, but all you have to do to run a php script from cron is to do call the location of the php installation followed by the script location. An example with crontab running every hour:
# crontab -e
00 * * * * /usr/local/bin/php /home/path/script.php
On my system, I don't even have to put the path to the php installation:
00 * * * * php /home/path/script.php
On another note, you should not be using mysql extension because it is deprecated, unless you are using an older installation of php. Read here for a comparison.