I want design my website to be a members only site. I want the site to be able to generate referrals URL whenever someone else i.e. whenever a new member registers.

I want the referral URL to be something like http://mywebsite.com/?ref=username similar to the liberty reserve referral system. I would also like to make the referral URL to redirect to my sign up page.

How can I be able to do all this?

Any ideas, someone?

@op
You have to code the website to achieve such result.
Is your website up? If yes what is the url?
You have to write a function that can achieve that result for you.