I don not have an X-Box myself, but from that I have been told you don't want to play HALO 2 on a Modded X-Box. What happen is that it scans your X-Box hard drive. And if it then detects a mod, it locks out your X-BOX LIVE so you can no longer play online.
Personally I think that sux as it's your console, you should be allowed to do what you want with it. Okay, VOID HARDWARE WARRANTY, but disabling your X-Box Live function I find is a little unethical IMHO.