Originally posted by stecal
It is not a bad idea to create a separate user, oracle9, who owns the 9i software. Your oracle and oracle9 UNIX users/accounts can be in the same groups (dba, oinstall). Creating a user, which is a one-time process, is much easier than changing ORACLE_HOMEs, which you may wind up doing numerous times as you go back and forth between versions.
During conversion, you will need to chmod your datafiles, control files, etc. Personally, I think that's a lot of extra work, but that's also your choice...