See the following article - its not a extended stored procedure, but involves returning a resultset.   I've generally opted for the extended stored procedure, because of the performance impact of doing anything significant with Oracle.

http://groups.google.com/groups?q=%22Umachandar+Jayachandran%22+%22SQL+SERVER%22+%22ORACLE%22+OPENQUERY&hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=OgiCJDW%23BHA.2552%40tkmsftngp05&rnum=2