Here is a very quick reply (The first very basic thing):
In 9i there is no EXCLUDE clause. To use EXCLUDE you have to use DATAPUMP.
In 9i :
1. Get the list of all tables by using :
select table_name from dba_tables where table_name not in (those 20 tables) ……and some more clauses here….
2. Now you have a list of all the tables that you want to import. Use TABLES= clause with imp : use $ imp help=y also
3. prepare a par file and do the import.