From the new version 0.9.8.1 CentOS Web Panel has built in function to setup quota on your server.
To enable quota on your server go to CWP.admin
- in the Left Menu --> File Management --> Disk Quota Setup
and click on the quota setup
You can also setup quota manually, here are detailed instructions:
http://forum.centos-webpanel.com/centos-configuration/how-to-setup-user-quotas/
For openVZ and virtuozzo VPS servers this needs to be enabled on the main node by your hosting provider.