Make sure all the same libraries are in the
same place. For example, on every machine, the Archicad Library should be in C:/Program Files/Graphisoft/Archicad 10/Archicad 10 Library
If you are also using an office library it should be kept either on a server or again, in the same place on every machine, in which case someone needs to make sure they are synced regularly.
And then project specific library parts should be kept in the same master folder as the Archicad file.
Check the CAD Managers forum for heaps more on library management:
http://archicad-talk.graphisoft.com/viewforum.php?f=37