You should be able to access the cubes just fine, the same way you can access a SQL 2000 database in SRS 2005. Everything SQL 2005 is supposed to be backwards compatible with reading SQL 2000 data.
Now, there are some tools that aren't able to be used with a 2000 database, like DBMail, but those are tools which look for specific stored procedures and values in system databases, etc. SRS is technically just looking at the data.
Catadmin - MCDBA, MCSA
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