Thanks Sweetpete for this one. Service Pack 2 (SP2) is a cumulative service pack that includes Service Pack 1 (SP1) functionality in addition to fixes for server issues that were previously available as Microsoft Quick Fix Engineering (QFE) patches. SP2 also includes a number of feature enhancements and utility updates.
You should download and install on all servers running Exchange 2000.
Exchange 2000 SP2 does not require an update to the Microsoft Active Directory schema, except for the Lotus Notes and Novell GroupWise Calendar Connectors that can be installed through a separate installation program.
For a complete list of QFE patches that are included in SP2, see article Q311456, "Exchange SP2 Release Notes," in the Microsoft Knowledge Base.