Thanks for the info.
I've been asked if we can do this without further purchasing of MS products plus the hardware

The WAN link would be via dsl line (8Mb) with Untangle boxes setup in router mode at both ends with Open vpn configured as site to site.
Ideally i see where you're coming from replicating between DCS and preferably using Cisco VPNs but unless the remote office becomes permenant then I don't think we'll see the cash for Server 2008 etc.
My only concern until further investigation is whether this will have a dramatic impact on the server/network at HQ?