#here we load php and get the physical address of the file
#0 2 * * * says that it should run in minute zero, hour two, any day of month, any month and any day of week
0 2 * * * /usr/bin/php /www/virtual/username/cron.php > /dev/null 2>&1
 
#my favorite, with wget the page is processed as it were loaded in a common browser
0 2 * * * wget http://whereismycronjob/cron.php