I spent quite a bit of time on this. I found BOL to be less than useful (dated information). I never a number of posts that indicated installing both 32-bit and 64-bit Oracle clients

I am listing my steps in the hope that someone might get some benefit from them.

Both of my database servers (SQL 2008 R2 and Oracle 11.2.0.1) are Windows 2008 R2 64-bit.

1) From the Oracle website download section, I down loaded from under the oracle database section the win64_11gR2_client and installed it on the SQL Server database server. I rebooted here (might have needed to do so).

2) I used Oracle Net Manger to configure the client. When tested I successfully connected to the target Oracle server.

3) Added a tnsnames.ora file (point to the Oracle target) in C:\oracle\product\11.2.0\client_1etwork\admin

4) Defined the Linked Server - I mapped specific logins; checked the Allow inprocess box under the OraOLEDB.Oracle Provider

Querying from the SQL Server server to the Oracle server was successful