Here is another note from Metalink(111942.1) which would solve your problem in TNS_ADMIN resolution :
TNS_ADMIN Resolution Order:
On Windows NT/2000, the precedence in which Oracle Net
Configuration files are resolved is:
1. Oracle Net files in present working directory (PWD/CWD)
2. TNS_ADMIN defined sessionally or by user-defined script
3. TNS_ADMIN defined as a global environment variable
4. TNS_ADMIN defined in the registry
5. Oracle Net files in %ORACLE_HOME/network|net80\admin
(Oracle default location)
Setting the TNS_ADMIN environment variable
From Oracle9i (9.x) onwards, Oracle Net Services is the current name for the
Oracle Networking product, formerly known as; SQL*Net in Oracle7 (7.x), Net8
in Oracle8 (8.0.x) and Net8i in Oracle8 (8.1.x). For consistency, the term
Oracle Net is used thoughout and refers to all Oracle Net product versions.
The TNS_ADMIN parameter/environment variable is used to explicity define the
directory location for Oracle Net to resolve where to find its configuration
files. TNS_ADMIN over-rides the default Oracle Net location.
For example, if TNS_ADMIN is set to ORACLE_HOME\test\admin, Oracle Net looks
for its configuration files in ORACLE_HOME\test\admin to make a database
connection or start other Oracle Networking products such as; the Listener,
Connection Manager, Names Server, etc.
TNS_ADMIN can be defined in the following ways:
Access the Windows registry i.e. click: Start > Run, then enter
'Regedit.exe' (or 'Regedt32.exe'). Add the TNS_ADMIN environment
variable to the HKEY_LOCAL_MACHINE\Software\Oracle[\Home[X]] key
by right mouse clicking, then selecting: New > Key > String Value.
Note: [X] is the Home Id for the ORACLE_HOME being modified.
If you are unsure where to set TNS_ADMIN in the registry, refer to
the ORACLE_HOME\bin\oracle.key file which provides the location of
the registry key used by executables within that home.
Setting TNS_ADMIN in HKEY_LOCAL_MACHINE\Software\Oracle[\Home[X]]
key over-rides the default Oracle Net location for products only
installed into that ORACLE_HOME.
By default, each time you install different Oracle versions, the
default location to which Oracle Net files are generated is the
ORACLE_HOME\network|net80\admin directory. Over time, these two (or
more) sets of configuration files may start to contain differing
information and entries.
In this case, you may wish to set TNS_ADMIN in the environment rather
than as a Home-specific registry entry (see below). This consolidates,
centralises and aids administration of Oracle Net configuration
files. However, be aware of syntactical differences and parameter
behavioural changes between different SQL*Net/Net8/Net8i/Oracle Net
Be aware that some Oracle product combinations may require, or be
better suited to, maintaining Home-specific versions of Oracle Net
configuration files. Examples include; Oracle Applications, Oracle
9iAS, Oracle Enterprise Manager (OEM), etc. If using combinations
of these products, exercise care so not to accidentally modify
the other ORACLE_HOMEs TNS_ADMIN location e.g. making a global change
that adversely affects Oracle Net connectivity of other Oracle
TNS_ADMIN may also be defined as a system-wide or global variable
within the operating system. To do so:
1. Logon as Administrator.
2. Click Start > Settings > Control Panel
3. Double click the SYSTEM icon
4. From System Properties, select Environment tab.
The Environment tab lists System environment variables defined by
Windows NT - these are the same no matter which user is logged on
to the computer. When logged as as a member of the Administrator
group, you can modify, add or delete values.
5. Highlight OS in the list of Systems Variables
In the Variable field you should see: OS and in the Value field,
the value: Windows_NT
6. Change the Variable from OS to TNS_ADMIN.
7. Change the Value from Windows_NT to the complete path were the
configuration files will reside.
For example: c:\orant\net80\admin
8. Click Set, then apply.
In the System Variable table you should now see the TNS_ADMIN
variable with the path to the location of Oracle Net configuration
9. Click OK to close window.
This setting will force all installed Oracle applications run or
launched from this server to use the same set of configuration files.
Note: Again, care should be taken when setting global variables,
particularly for multiple ORACLE_HOME environments. This action
will modify other ORACLE_HOME's TNS_ADMIN locations and may
adversely affect their ability to connect.
TNS_ADMIN may also be defined for a given Command Prompt session.
C:\> set tns_admin=c:\temp
In this case, the value of TNS_ADMIN is only valid for the life of
the Command Prompt session. Once terminated, the value is lost.
Hope it helps..