Can anyone help me?

I have a simple chat system running here : http://www.aviz.co.uk/chat

At the moment, anyone can log in, but i need to make it so there is a database of some sort which has a list of users and their passwords in, so they have to log in like on this site :

http://www.oscarjsweb.com/chat/

Anyone any pointers as to how it can be done?.. I'm no asp Genius :(

Any help appreciated.

Cheers

Andy