[Samba] Linux users and Samba 4

[steve]

I have a LAN of linux and win7 clients currently with Samba 3.6 and 
LDAP. Linux users authenticate against LDAP and are placed in their 
nfs'd /home folder. The same user can also logon to windows. His roaming 
profile is stored in his /home folder. (something like .msprofile_v2)

How do I transfer my current Linux/Samba 3/LDAP users over to 
Linux/Samba 4?

Thanks.
Steve.