First off, I want to pass my sympathies on to the crew at Bungie on having their magnum opus, "Halo 2," leaked to the Internet.
On the upside, I don't think that it's going to affect your sales at all. First off, it's in French with English subtitles. Second, it requires a lot of extra hardware installed on the Xbox for it to work. Finally, they won't be able to play on Live with it.
One thing I really admired about "Halo" was the storyline. Back when the crew in Salt Lake was working on "Amped," we got the occasional builds of "Halo" into the Salt Lake office.
I beat the game three times before it was released, but never got to see the ending. The reason: external builds had the cutscene that was supposed to occur as you start up the ramp to the shuttle removed. Crossing the trigger plane caused the game to freeze.
When I got my limited edition green Xbox two days before the Xbox's release date, the first thing I did was pop in "Halo." I played it non-stop and loved every minute of it. Finally, I got to the end. Hearing the explosions all around me over my home surround sound system made the ending feel more vibrant and alive to me. Finally, with 21 seconds to spare, I crossed the trigger plane...and found an ending that I had no complaints about.
So I'm with Bungie on this one. Don't tell people anything about the leaked version. I want to be just as surprised as I was by the first one.