Scenario is to use a source code repository as usual except at periodic intervals, take a backup of the delta changes and copy them over to a remote location which should bring it to the same state as the source, the reverse should also apply assuming that no new changes have been committed to the 1st instance in the interim
I hope this is clear, i have used vss mostly from a user perspective, never from an administrative standpoint so pardon my ignorance
UPDATE: * The solution should ideally be open source or low cost * Note replication is to be done via File Copy/Paste operation ( with file transfer via email etc. )