I have used p2p programs but they can be well dodgy for the state of your pc and security.
I used SopCast for the Ryder Cup and watched the coverage from the Canadian Sports Network (CSN).
The day after the cup, I fried my H-D and re-installed Vista.....then all my programs....then all my documents....then re-set permissions and protocols....time consuming, but worth it. p2p can be great, but almost any file on your PC could potentialy be broadcast "in reply" to p2p communications.