This is a very happy song called "Yatta!" The phrase was made universally famous by Hiro from Heroes, but it's long been a part of the expression of joy in Japan. Part of this song's chorus goes: Yatta! Yatta! All you need is one leaf.
I think somebody linked to this video in the comments somewhere, though I apologize because I can't remember where it was.
There is a cool retrospective on NicoDouga with lots of people doing Yatta! around the world: http://www.nicovideo.jp/watch/sm1446231
I'm the black box #01 in it. XD
Posted by: Jeshii | September 17, 2008 at 08:14 PM
I love this song for a long time.yattayatta.
Posted by: kanatin | September 17, 2008 at 09:40 PM
holy crap!
I think I need to sit down.
Posted by: poldevia | September 18, 2008 at 10:00 AM
Just for those beeing curious: The song is performed by the comedy group "Happatai". Always good for a laugh. :)
Cheers
Posted by: Seelan | September 19, 2008 at 06:53 AM