anonymous user in windows

Hello,
Why does the O.S. need anon. users?
Are there differences in the need for Anan. Between XP Home and XP Pro?
What happens differently with Anan. user on a Windows 2000 network vs. a Peer to Peer network

1) what is its purpose,
2) does it have unique characteristics under different operating systems,
3) does it have unique characteristics under different LAN configurations,
4) what events are included in the event logs, and
5) how to protect internal and external systems from hackers that take on anonymous user rights.
thanks for the help