username log in, ideas please...

Looking for a bit of advise please.

I am part of an online club, I won't go into details right now, each member
has a Username which they give to possible new members and they can visit
the site and when they input the username given to them they will be
directed to a page with the contact details and signup codes for the member
who told them about the site.

I have my doubt's about some of the information this site is providing and
would like to create another site just for my team, I think I can do it
better.

But, I don't know a way to do the log in bit, I could do it the subweb way
but this will need a username and password and I would like to do it just
with a username as above.

My other thought is if I can not do it this way to have one page with a list
of all my members and then when a new prospect is directed to the site they
look down the list and click the name of the person who sent them to the
site, but would prefer to do it the other way cos I think it would look my
professional.

Hope someone can help

Thanks
John