thanks for the reply, sorry about the delay, been stuck in a room all week trying to get this up and running.
Yes, it is 3 projects or a few stages at least.
1- To determine the directory service that will hold all our user records. I have managed to get SAMBA 3.0.28 running on an OpenLDAP backend where we have 1 PDC and it replicates changes to our BDC (more BDCs to come, as all our other sites will act as BDCs). The following doc helped alot.
2.- So now we can register onto the domain and connect to either the BDC or PDC which is where we were trying to head.
3- Once I have this all rounded off and tested thoroughly, I will then look at rolling this our site by site, hitting small sites first as we can test in the live environment.
Our biggest hit with this solution was that our Global partners wanted us to connect to their Active Directory in order to access their applications. Where I have setup a trust account on SAMBA and setup a trust (outgoing) on the AD. Now we can add users into a group that the AD admins can allow access to the applications that they require us to access without them needing to setup accounts and handle passwords etc...