test@9i > desc user_users
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ------------------------------------
 USERNAME                                              NOT NULL VARCHAR2(30)
 USER_ID                                               NOT NULL NUMBER
 ACCOUNT_STATUS                                        NOT NULL VARCHAR2(32)
 LOCK_DATE                                                      DATE
 EXPIRY_DATE                                                    DATE
 DEFAULT_TABLESPACE                                    NOT NULL VARCHAR2(30)
 TEMPORARY_TABLESPACE                                  NOT NULL VARCHAR2(30)
 CREATED                                               NOT NULL DATE
 INITIAL_RSRC_CONSUMER_GROUP                                    VARCHAR2(30)
 EXTERNAL_NAME                                                  VARCHAR2(4000)

scott@9i > select table_name,tablespace_name from user_tables;

TABLE_NAME                     TABLESPACE_NAME
------------------------------ ------------------------------
DEPT                           USERS
EMP                            USERS
PLAN_TABLE                     USERS

scott@9i > create table sample
  2  (id number)
  3  tablespace tools;

Table created.

scott@9i > select table_name,tablespace_name from user_tables;

TABLE_NAME                     TABLESPACE_NAME
------------------------------ ------------------------------
DEPT                           USERS
EMP                            USERS
PLAN_TABLE                     USERS
SAMPLE                         TOOLS

scott@9i > create table sample (id number) tablespace users;
create table sample (id number) tablespace users
             *
ERROR at line 1:
ORA-00955: name is already used by an existing object

scott@9i > create table "sample" (id number) tablespace users;

Table created.

scott@9i >  select table_name,tablespace_name from user_tables;

TABLE_NAME                     TABLESPACE_NAME
------------------------------ ------------------------------
DEPT                           USERS
EMP                            USERS
PLAN_TABLE                     USERS
SAMPLE                         TOOLS
sample                         USERS