SQL Navigator does not officially support ONAMES connections. However, there is a workaround available for the Windows 2000 and XP environments that allows SQL Navigator users to connect using the ONAMES configuation. Unfortunately, this workaround does not work in the Windows 2003 environment.
For Windows 2000 and Windows XP environments:
1) Exit out of SQL Navigator.
2) Modify your SQLNet.ora file as follows:
NAMES.DIRECTORY_PATH = (ONAMES, TNSNAMES)
(ADDRESS = (PROTOCOL = TCP)(HOST = <name of the host>)(PORT = <port number>))
3) Rename tnsnames.ora file from your Oracle \bin directory.
4) Restart SQL Navigator and connect to your desired database server.