Are you using Access data Projects (ADP) or MDB files?
IF ADP's then you should be aware that Access 2000 adp's were not designed for SQL 2000 let alone 2005.
You have already identified a possible solution -- standardize everyone on Access 2003 or later. The other option which is one that should be done anyway to speed up object name resolution when parsing queries and that is to ensure that every object reference is qualified by owner name.
How are your access 2000 using authenticating? Windows or SQL? If SQL are they all using the same user or different users?
David Lundell
Principal Consultant and Trainer
www.mutuallybeneficial.com