How does 6-degrees work?

As if you couldn’t tell, I’m a 6-degrees fan boy. For all the programmer types out there, how does the database side of the whole concept work. For example, on Friendster I see:

You <-> Jolene <-> Michael <-> Ricky <-> Kelly

I’d assume that all the users are stored in a table, with a column containing friends. Let me know if I’m off base here. To make things simple, lets say the table looks like this:

ID | USERNAME | FRIENDS

In MySQL, how would you get to Kelly? It might be fun to do a little open source social networking. Friendster is going to go pay soon, and it’s already slow. Hipstir is fun, but still not open source.