please how can i create a site that members can reffer others with their own unique link for example www.mysite.com/memberusername ,i intend to use this for a refferal program.any help will be appriciated

If I understand you correctly, u can use a "tell a friend" form:

The form wd hv 4 fields (for instance): your name, your email, friends name, friend's email. when you click submit, (if you are using PHP), use the mail() function to send an email to your friend and stating in the message part:

- your name
- your message beginning with something like, "check this site out" or whatever goes there.

Of course, if you don't want to go thru the hassle of doing it yourself, you could use whatever 3rd party app is out there.

I have done something like this for a client.
check it out at: http://www.15pointsclub.com
Checkout my site: http://www.netxpertsolutions.com for more info.
You can call: 08037184179

or do u mean that you want users to have their own customized directory under the site? Say for example, I, goldincome and yawa registered, we should hav e ursite.com/kehers, ursite.com/goldincome, ursite.com/yawatide - with each containing our personal profiles? Just like myspace and twitter?
The trick to that is something called url rewriting. Here is a search result from Google as regards that. And Im hoping it will help.