By the looks of things, it seems no Xbox OG emulator can run the original Halo. I might be wrong, but the best I could find was one emulator that can play a single level. Xbox emulation is still in its infancy, so you might want to give it a few months.
"NintenDON'T sue me please haha"
You guys should add the original Halo as it is a blast to play local vs matches and there are many roms out there bundled with viruses, spyware etc.