You'll need to install the two clients into separate Oracle Home locations, for example I've gone for C:\OracleHome
and C:\OracleHome32
Then set up an Environment Variable, called TNS_ADMIN with the folder that contains your default TNSnames.ora file as the value (for me it is C:\OracleHome\network\admin
)
Keep your preferences in PL/SQL Developer, and make sure you also specify the OCI library (mine is C:\OracleHome32\oci.dll
)
Finally, using regedit.exe, add a second key under ORACLE (HKEY_LOCAL_MACHHINE\SOFTWARE\ORACLE
). I've called mine KEY_OraClient11g_home1 and KEY_OraClient11g_home2. Create the same 4 strings in the second key, with the appropriate changes to the data (e.g. ORACLE_HOME should have C:\OracleHome32
as it's data field in my example)
Restarting all applications should now let you use PL/SQL Developer seamlessly, whilst also defaulting to the 64-bit Oracle home for your weblogic application.