FTP Access

Hi
We recently setup our new FTP server. We have number of clients from different places who update files through FTP. I have to proibit client access by seeing other client root directory. Here is the problem when they logon to our ftp site, client should be able to see only his directory and subdirectories not to other client directory. How to setup. Help will be appriciated.

Ex:
root directory
(XYZ)
Below this Client1, client 2, client 3, etc., sub directories

Client 1 should see only client 1 directory
he should not see client 2, client 3 etc directories.

If it can be done by scripting please send me the sample scripts.

Thanks