At least, that's what Brian Ashcraft at Kotaku says about the pre-Tokyo Games Show press event held by Microsoft, where they did show some Halo:

Now, they are showing a Halo 3 trailer. Because, you know, the Japanese really love Halo. It's a new trailer! They showed the Japanese TV ad, too. The Halo 3 Xbox 360 will be open priced when the game goes on sale here.

Check the Kotaku story for their coverage of the event.

Kotaku has the story that Yahoo will be hosting two new exclusive Halo 3 videos, Museum and Believe, this week.

Both will debut at 9 PM Pacific Time; Museum on Wednesday, and Believe on Friday. Looks like live action and commercial footage, rather than in-engine cutscene or gameplay.