Linux Directory Services?

m0rph asks: "My company is building a Linux web cluster solution. We are currently discussing using Open LDAP for user authentication (for ftp http etc). I have been reading recently about the NDS port to Linux. This has raised some questions to me. In reading the NDS-Linux How-To the document states the you can use NDS in conjuction with Open LDAP. Being new to directory services I am wanting to know how does NDS differ in function from Open LDAP or other directory services? Is anyone using this same sort of method for authentication? and if so what are you using? why would you use a directory service like NDS with Open LDAP? also can someone can reccomend good documentation or a book that you have had good results with? "