I just did a search in Google for "php user registration form" and it came up with sites like these http://www.olate.co.uk/articles/185 or http://uk.youtube.com/watch?v=OQ14NjbEXJM. I haven't looked through them but they seemed to be going along the right lines.

Assuming your OK with PHP you just need to present a form where users can put in their details i.e. name and email. At this point you would often have an image containing text that the user needs to type in - this tends to stop robots from setting up 1000's of accounts. Normally you would then email them a random password. Then they login with this password and change it to a password of their choice.

Mike