If you get a copy of the resource kit, included in msdn and technet subscriptions, there is an electronic interactive view of the system tables.
sysobjects and sysindexes are local to each database, sysdatabases is common to the server - I can't think why you'd really want to attempt to make such a join - I suppose a profiler trace - anyway you'd have to infer the joins as sysobjects does not contain a database id as it knows where it is.
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