this is for those other newbies like me who could not find the crontab for the users in the ISPConfig (it took me a while searching for it):
1. Goto ISPManager=>Sites Folder=>Click a User website.
2. On the Basis Tab below it you will see a "Cron Jobs:" check box, check that.
3. Then go to "User and Email" tab.
4. Then click a user, for me it's web1_user.
5. Check "Cron Jobs:" checkbox and save, then go back to that section again there you will see a new Cron Jobs tab.
... just trying to help