SQL & PL/SQL

This is my firs time dealing with oracle, am installin 10g release 2 on a xp box but i keep on getting this msg, *** ORA-12560: TNS:protocol adapter error *** i really need help cuz i have homework due on Saturday i i can't access the data base. I went to other forums but nothing seams to work .. So far i did this

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copied from another forum *
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This error can be caused because of many reasons.
First thing you need to do is to check the files tnsnames.ora and listener.ora are available in (directory:\oracle\ora92\network).
If all these files are there then check if the files contain the correct information.
Next go to the MYCOMPUTER rt click on the icon
go to the properties
select advanced tab
select environment variable
in the second pane at the bottom
select add
in the first box write Oracle_sid
in the lower box write SID(whatever you have given the name to be when you created the database)

If you still have any questions you may mail again.