Here's the link: http://www.nintendo.co.jp/wii/rmgj/index.html
Breakdown for those who don't know japanese or bother to keep a status bar to read the link's url address:
Co-Op/Assist Play: http://www.nintendo.co.jp/wii/rmgj/assist/index.html
In-game Action/Movies: http://www.nintendo.co.jp/wii/rmgj/action/index.html
Prologue/Story: http://www.nintendo.co.jp/wii/rmgj/prologue/index.html
Videos on the website have been posted on Gametrailers.com, Here are the links:
[From Prologue Section]
Japanese Prologue: http://www.gametrailers.com/player/25847.html
[From In-game Action/Movies Section]
Honey Bee Gameplay: http://www.gametrailers.com/player/25851.html
Boo Mario Gameplay: http://www.gametrailers.com/player/25856.html
And more...
I am a PC gamer, and also have a NDS now, but without access to a Nintendo Wii until End of 2007.
Currently playing: Super Smash Brothers Brawl(Wii), Mystery Dungeon: Shiren the Wanderer(DS), Dragon Quest Heroes: Rocket Slime (DS), WiiFit(Wii)
Games Recently Beaten: Final Fantasy Crystal Chronicles: My Life as a King (Normal; Very Hard after the next DLCs become available)
1 word: RTFA