One of the nice tools that is provided with SQL Server 2005 is the TableDiff.exe table comparison tool. It allows you to compare the data in the same table on different servers or instances. Below is an expample that compares the data in "table1" and places the results in the table "Table1DifferencesServer1Server2". This command needs to be run from the command line, in the directory where tablediff.exe is located.
C:\Program Files\Microsoft SQL Server\90\COM> tablediff -sourceserver "server1" -sourcedatabase "database1" -sourcetable "table1" -destinationserver "server2" -destinationdatabase "database1" -destinationtable "table1" -et Table1DifferencesServer1Server2
More info can be found on BOL http://msdn2.microsoft.com/en-us/library/ms162843.aspx