adding users to Windows 2000 server

Without doing your homework for you, I can point you to:
www.microsoft.com/technet
where you can search for topics and keywords of interest.
For adding an account to a domain, look at the management console.
For dial-in users, look at RAS and radius.
You might also search Techrepublic for the keyword 'radius'

Good luck.

One: For IIS (accesed from internet) you do not need to set up a new user. It will use the anonymous login.
TWO: If you need some internet users to access some pages depending on some privilege, you must do one of this 2 things.
a.- Create your own database and validation method (the best for holding thousands of users, and will let you save some other usefull info like, age, email, etc, etc.)
b.- Define the user like a new win2k user, assign him a password and give access from the iis environment.

good luck