I need options to query multiple SQL servers

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http://serverfault.com – In recent months, we have converted to a new software application. The migration team (vendor) left the old database intact. They converted some of the old data to an "archive" database using the new-vendor's database structure. (That way the new software can be used to access the archived data--thereby eliminating the need for old-software licenses.) Since the conversion, our company has entered data into the new database. I need to pull data from all THREE databases (on two SQLserver2005 servers). I would like to use a "union" query to pull all the data and automatically eliminate any dupli (HowTos)