User Account Management?

Jeremy Welling asks: "I work in a corporate data center with all the major Unices present. Currently we are using a third party product to manage user logins and authentication. In our goals for 2002, we want to move off that product, and the current plan is to go to NIS. Due to the inherent security holes in NIS, I am investigating using LDAP. We would also like to tie this into the NT domain logins. My question is, how difficult is this to do, what LDAP server software would be best, and what OS platform should we look at?"