So I am assuming you have 2 tnsnames, one in each Oracle_Home directory. Have you tried just opening a sqlplus connection and see if you could connect to the Oracle9i db. I would also try opening sqlplus from the Start->Run so as to also see which one it brings up…the 7 or 9 version.
I have a feeling this has something to do with which Oracle home it is using. Hope this helps, if not, let me know what you found from the suggestions above.