Refer friends after Registration

[it_pimpin]

I would like to request a modification whereby immediately after new members registers on a forum, he/she before the page where they are given the option to Modify User Profile are given rather the opportunity to invite 3 or more friends to the forum like is obtainable on sites like myspace/ digg etc etc.

The modification should be quite simple to do and it should run on PHP and use the php sendmail class.