I am making a program in Java that I hope to have record the stats after a game (Halo3 from the scoreboard). Will it be possible to just view those stats through sniffing the packets? Not over Xbox Live just on system link. Has anyone done packet sniffing on system link?

xbox live data is encrypted, i dont know for sure but assume it would be the same for system link so as not to leave any security holes for us to try and exploit.

That doesn't make much sense really, connection to xbox live is handled via kerboros authentication, and that's presumably how the session keys are passed, how would that be done over system link? Symetric key maybe, but that would mean all consoles have the same key...

According to this system link uses Diffie-Hellman key exchange to establish session keys - presumably with certificate based authentication to avoid man-in-the-middle attacks.