Hello, someone try this path?
I ask the same question on IRC and got this reply:
Q: hello, Is there a way to introduce a Zentyal in Win2008 SBS network and after kill Win and stay only with Zentyal?
A: yes, you can join the zentyal box to the domain, then promote (that's the technical term) it to PDC. once the zentyal box is the primary, you can remove the windows dc
So the right procedure is: add BDC to Win domain for get all LDAP informations, demote Win server and promote Zentyal?