ehensley is correct, except for the spelling of the file name. The file TNSNAMES.ORA can be in multiple locations and does not have to be in a specific path that is known by the Registry. It does depend on the file structure where the program was originally installed.

We had this problem a couple years ago. What we did was to make an installer that would search about 5 known install locations and replace any and all of the known file locations.

I would not recommend searching the entire drive and doing replacement as it will take a VERY long time to search complete hard drives. I would do a little research as to the most common install locations in the past and then look for the file in those specific areas and update it as needed.

What about the LISTENER.ORA and SQLNET.ORA files? They may also need to be updated.