CRON job for codeigniter
You can find some more information on making CodeIgniter CLI-accessible here:http://phpstarter.net/2008/12/run-codeigniter-from-the-command-line-ssh/
Next step is just using crontab -e to set up the cronjob.
This might not be what you're looking for, but it works just fine for me:
Create your CRON job logic as a 'normal' controller function.
Then, in your standard, non-CI, PHP cronjob file just load the URL via
file_get_contents('http:example.com/cronjob/');
This will treat the URL as being hit just as by any other user and the entire CI framework will be at your disposal.
If you are looking on how to create cron job, then have a look at this:
http://www.unixgeeks.org/security/newbie/unix/cron-1.html
But if you mean how to put expired users into another table, then you should show your table structure.