SQL> def month=10
SQL> def year=2008
SQL> with 
  2    lines as (
  3      select 7*(level-1) d
  4      from dual 
  5      connect by level <= to_number(to_char(last_day(to_date('&month&year','MMYYYY')),'WW'))
  6                          - to_number(to_char(to_date('&month&year','MMYYYY'),'WW'))
  7    )
  8  select to_char(to_date('&month&year','MMYYYY')+d,'YYYYQMM') R1,
  9         to_char(to_date('&month&year','MMYYYY')+d,'YYYYWW') R2
 10  from lines
 11  /
R1      R2
------- ------
2008410 200840
2008410 200841
2008410 200842
2008410 200843

4 rows selected.

FOO SCOTT>l
  1* select 1 from dual where sysdate > '01-NOV-2008'
FOO SCOTT>/
select 1 from dual where sysdate > '01-NOV-2008'
                                   *
ERROR at line 1:
ORA-01858: a non-numeric character was found where a numeric was expected

FOO SCOTT>create table t_date (date_id date);

Table created.

FOO SCOTT> select * from t_date
  2 where (date_id between '01-OCT-2008'and '31-OCT-2008' )
  3 and trim(to_char(date_id, 'DAY')) = 'FRIDAY';

where (date_id between '01-OCT-2008'and '31-OCT-2008' )
                       *
ERROR at line 2:
ORA-01858: a non-numeric character was found where a numeric was expected

SQL*Plus: Release 10.2.0.1.0 - Production on Fri Oct 24 19:19:31 2008

Copyright (c) 1982, 2005, Oracle.  All rights reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL> alter session set nls_date_format='MM/DD/YYYY';

Session altered.

SQL> SELECT SYSDATE FROM Dual;

SYSDATE
----------
10/24/2008

SQL> create table t_date (date_id date);

Table created.

SQL> SELECT *
  2  FROM   t_Date
  3  WHERE  (Date_Id BETWEEN '01-OCT-2008'
  4                          AND '31-OCT-2008')
  5         AND TRIM(To_char(Date_Id,'DAY')) = 'FRIDAY';
WHERE  (Date_Id BETWEEN '01-OCT-2008'
                        *
ERROR at line 3:
ORA-01858: a non-numeric character was found where a numeric was expected

SQL> alter session set nls_date_format = 'DD-MON-YYYY';

Session altered.

SQL> SELECT SYSDATE FROM Dual;

SYSDATE
-----------
24-OCT-2008

SQL>  SELECT *
  2   FROM   t_Date
  3   WHERE  (Date_Id BETWEEN '01-OCT-2008'
  4                           AND '31-OCT-2008')
  5          AND TRIM(To_char(Date_Id,'DAY')) = 'FRIDAY';

no rows selected