Here is a pretty complete walk-through implementing the Oracle OLE DB driver on 64-bit SQL 2005 connecting to Oracle 10g via a Linked Server. I would expect the steps to translate to SQL 2008 and Oracle 11.2 unless the Oracle Drivers took a step backward.

http://www.mssqltips.com/sqlservertip/1433/how-to-setup-linked-servers-for-sql-server-and-oracle-64-bit-client/[/url]