Samba 3 allows samba accounts to not have corresponding unix accounts. This is the first time a Samba has allowed this. However, I've not set it up so I won't go into that.
So this will - at first anyway - discuss setting up Samba 3 + LDAP in an environment where you already have LDAP handling your unix accounts. See LDAPNotes for information on that.
Debian users: Samba.org has Woody packages for Samba 3; you can get it out of testing/unstable otherwise.
The Samba 3 packages have a set of smbldap-tools - you really should set these up.
Now go and read the excellent 
LDAP-SMB-2.2/HEAD HOWTO.
As I don't have much time atm, I'll leave it here. I know this page contains nearly 0 content, but I'll pad it out when I get more time.
Samba 3 has been released now. It has much better ActiveDirectory support, and also boasts a completely rewritten ldap schema, just to annoy those early adopters who played with the alpha series. They do provide a script to convert the two however :)
Just stumbled upon this link: http://homex.subnet.at/max/ldap/ for Samba and LDAP. http://samba.idealx.org/ has a good howto and some smbldap-tools scripts for user administration.
3 pages link to Samba3LDAP:
