Using Oracle 8.0.5 in Windows 2000 Server.

I created a DB, and I check it correctly by using SQL*Plus with my user/password.

But I've got a problem when trying to create a service.

I modified LISTENER.ORA, adding:
(ADDRESS = (PROTOCOL = IPC)(KEY = MY_SID))
and
(SID_DESC = (SID_NAME = MY_SID))

I modified TNSNAMES.ORA, adding:
MY_SERV.WORLD =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(Host = 127.0.0.1)(Port = 1521))
(CONNECT_DATA = (SID = MY_SID))
)

But when trying to connect this service (for instance, using 'TORA' or testing with 'Oracle Net8 Easy Config') I get this error message:
******
ORA-12505: TNS:listener could not resolve SID given in connect descriptor
******

If I type in MSDOS, I get
> echo %ORACLE_SID%
MY_SID

And I'm able to connect via SQL*Plus... what am I doing wrong?

Any suggestion is apreciated. Regards and thank you very much.