LDAP Server on Linux

Hi,

I'm here because I don't know much about LDAP so here goes my questions and concerns.

I have a couple of RedHat Enterprise Linux boxes and a Solaris 8 box that all run Apache. I'm interested in how I can set up a LDAP server so that all of my servers can access user accounts. These accounts will be used for web site aunthentication. Now the question that I have is that is it possible to install and configure LDAP on the same INUX box that houses my websites or is it better that I have a separate LDAP server. What are the pros and cons? What are the hardware requirements?

Currently my linux box retains user information in flat files, I know it's not a very effective solution...one reason why I'd rather configure LDAP but I just don't know where to start.

Second and actually the most important is that I need to migrate Sun/iPlanet's directory server to Linux/Apache. But it's impossible or highly unlikey to migrate the diretory server to flat files. Another reason why I'm trying to set up an LDAP.
Will it be possible for me to migrate the user accounts once I have a linux LDAP server installed? Or will I be spinning my wheels?

I sure would appreciate it if someone can provide me with some insight. Thanks a lot.