Hello,
This is probably because of the security context that you are using to access the Linked Server. For example, are you passing through the Windows/SQL Login that is accessing the SQL 2000 Server, or using a single SQL Login, configured in the Linked Server properties?
Regardless of which, the chosen Login needs to have access to the DB on the SQL 2005 Server, and then have permission to access the “customers” table.
Hope this helps.
Regards,
John Marsh