As you yourself say, Discoverer 9.0.4 is long de-supported and is not certified on Windows 7. So when you say the folks at Oracle are less than forthcoming that is a little unfair as a) you are using an obsolete product, and
you are attempting to install it on a platform for which it is not certified.
Did you try installing it into XP Mode of Windows 7? If you tried it in the native OS I don't think there is any way that it will work. Even though it is not supported on Windows 7 it was supported in XP so that is, I believe, your only chance of getting it to work.
Also, what version of the database are you trying to connect to? Discoverer 9.0.4 came out long before some of the newer versions so it does not come with the install scripts for the EUL user like the newer ones do.
For an Administrator the newer editions, aka newer databases, need these privileges:
create user &username identified by &password;
grant connect, resource to &&username;
grant alter any materialized view to &&username;
grant analyze any, create any materialized view to &&username;
grant create procedure, create role, create sequence to &&username;
grant create session, create table, create view to &&username;
grant drop any materialized view, execute any procedure to &&username;
grant global query rewrite to &&username;
grant select any table, unlimited tablespace to &&username;
grant execute on sys.dbms_job to &&username;
grant select on sys.v_$parameter to &&username;
Can you check what was granted to your user and see if any of the above might help?