Not sure if you configured the TNSnames yet?
a few guides below:
http://www.ideaexcursion.com/2009/01/05/connecting-to-oracle-from-sql-server/
http://support.microsoft.com/kb/280106
http://www.sqlmag.com/article/sql-server/setting-up-an-oracle-linked-server49687
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This thing is addressing problems that dont exist. Its solution-ism at its worst. We are dumbing down machines that are inherently superior. - Gilfoyle