Member Referal?

I'm not sure exactly how this would work out, but I know it's doable.

What I'm looking for is a member referal system. It can work either one of two ways.

A) Signed up member sends non-member a link. Non-member clicks link, registers on website, and it is logged in the database that this user registered thanks to the link of the already registered member.

B) A simple userfield to enter a signed up members username.

The reason I'm looking for something like this is because I want to add incentives to my website. It is a gaming community, and I want to add things to it by the amount of referrers such as private game servers for these registered members, higher priority notifications on what's going on, etc, etc.

I'm not saying you have to build an insanely large infusion just because I brought it up. I did a quick search but I did not find anything. Going to go smoke a cigarette then check phpfusion-mods.net - I know Diemux has loads of infusions waiting for me over there lol