Paul,
The Moveallreplicas.ps1 indeed MOVES the replicas from one server to the other. Actually, it just updates the replica list on folders that you run it on and then the public folder replication takes care of the rest. The end result though could be that replicas could be moved from one server to the other, and original server would have no more replicas.
Note though that your clients should still be able to access the PF content even in that case. You can test this by creating a folder on E2007, with replica on E2007 only, drop some content in there and see if E2000 clients can access it.
If you need to just add a server to the replica list, check this page out:
http://technet.microsoft.com/en-us/library/aa997966.aspx