Thanks for all the responses.. well I did warn him about not downloading movies, and he stopped for a bit, and now he's started again. The point is, that I can't kick him out. Its a family thing, and besides, I'm not the type of person to kick out a person anyway. I'd rather change some router settings so he can't connect to P2P hosts as a few people have explained.
I travel most of the time, and I have a Cingular data card (with the $80 per month plan) for use with my AMD laptop, but when I'm home, of course I use the DSL with my macbook. And recently, I discovered much to my anger, that my surfing speed was reduced to 42.5 kbps. I went to his room and he was using Limewire with a million downloads going on. Of course, when I turned his limewire off, my speed was back to normal.
I do have access to the dsl router settings (my login and pass) How do i block his access to Limewire? I can then rub my hands in glee and watch as he can't connect 😛