Oracle version 8.0.4 and onward are multi-home aware. In other words, for version 8.0.4 or later, place each oracle installation into its own ORACLE_HOME.
The non multi-home aware components for Oracle8i (all releases) are:
Oracle Performance Monitor for Windows NT.
Oracle Objects for OLE (OO4O).
Oracle Provider for OLE.
Oracle ODBC Driver.
Oracle Enterprise Manager.
Oracle SNMP Agent.
All products that depend on any of the above components
If there are no previous versions of Oracle installed or non multi-home components have not been previously installed, Oracle multi-home issues on Windows do not exist. Continue by going to the next step.
If there are non multi-home components which have been previously installed, there are two choices:
Uninstall the currently installed non multi-home aware components. Afterwards, install later versions of the components.
Leave the currently installed non multi-home aware components in the system. This means that the Oracle Universal Installer (OUI) will detect that these components are already installed and not display the newer versions of these components for installation.
For further details, refer to: