I've recently been looking at a similar problem - approximately 25 databases all with links into other databases, and we can't upgrade them all to 2008 at once. sp_depends is not accurate enough when dealing with objects in other databases, or via linked servers.

Our solution has been to restore all databases into a development 2008 environment and query the new sys.sql_expression_dependencies view. It's not perfect, as Lowell mentioned, as it can't detect dynamic SQL, but it's a lot better than the 2000 version of sp_depends.