Hi,
Connect as SYSTEM user and run the pupbld.sql script which is there in $ORACLE_HOME/sqlplus/admin directory.This script creates the PRODUCT_USER_PROFILE table which can be used to disable some commands for a particular user at SQL*Plus prompt.
In case of any help please be free to ask me at [email protected]

Regards,
ROhit Nirkhe,Oracle DBA,OCP 8i
[email protected]