The Paavo system is named after the great Paavo Nurmi who ran way way back in the day (like when XC was an Olympic event!). I don't know the specifics, but its probablly not what you want to do kid. I'm pretty sure it involves going out and just about every day and running pretty hard. Its basically like doing tempo runs on your easy days and then sandwiching workouts inbetween. There are some successful variations of this system, but in the long run I personally think it burns runners out. Again, I really don't know much about the Paavo system, except that its old, and perhaps involved a lot of specific heartrate training levels (that were used every day). I might be making that last part up..but I thought I remember reading that somewhere.