Hi,
There is no need to put the path of TNSNAMES.ora file instead you will need to enter TNS name username and password. You can check the connectivity using sqlplus command from prompt. Open command prompt and type sqlplus <username>@<TNSNAME> press enter. Type in the password and try to connect. If this connection is successful then you need to enter same TNSNAME, username and password while installing CRS 2011.
Also you should have 64 bit Oracle client with same version as that of Oracle database server installed on CR server.
Regards,
Hrishikesh