Hi Thomas Preethi,
Though you have installed Informatica clients on 64bit machine, application is 32 bit. So you have to create 32 bit DSN. Only 32bit ODBC DSN will be visible in the clients.
In addition to the post of Smitha.
The repository connections in the workflow manager must be configured to use the 64-bit odbc connections on the server(s). The server is using the 64-bit odbc connections at run-time.
The Designer client is only using 32-bit odbc connections to import the structures of the tables/views and to preview the data.
The PowerCenter client application is of 32 bit and hence it has access to 32 bit ODBC administrator only. There is no way for the PowerCenter client to access 64 bit ODBC administrator.
As far as the DSN is concerned (to import the tables), it is recommended to use the Informatica Data Direct drivers to import the tables rather using the DB Client native drivers.
For Oracle, you can use the Data Direct Wire Protocol for Oracle; available in the 32 ODBC Administrator to create the DSN and use the same to import the tables into the Repository.
Hope this helps.