I have three linux servers in the system and want to use LDAP to authenicate each of them , but I am not familiar with it, is there any doc. have step-by-step procedure that to setup it ? thx in advance.

Check if you have a "samba-docs" package. It should include either a postscript or pdf version of the Bruce Peren's series book, "Samba 3 by Example" by John H.Terpstra. Chapters 6 and 7 cover ldap and the idealx smb-ldap scripts.
The network in the example uses OpenLDAP for the PDC server in a 500 User network. Chapter 7 deals with a sample 2000 user distributed network with a master ldap server and 4 ldap slave servers.

Also google for the terms "redbook ldap". One result is this "Understanding LDAP" by IBM: http://www.redbooks.ibm.com/redbooks/pdfs/sg244986.pdf

This Howto deals specifically with Authenticating with OpenLDAP and PAM: http://www.imaginator.com/~simon/ldap/

With this link, you may have found the mother lode: http://www.bind9.net/ldap/