http://www.gametrailers.com/
Under the 'newest media' scrolling section, it currently is on the 2nd page. It is a simple demonstration of how you can mess around creating things in this little gem of a game. The video I've seen before was 4 player co-op through a platform level...really cool thing is you can make your own levels, and share them on PSN...apparently you can rank them and they will be displayed youtube-style ready to download.
Anyways, check out anything related to this game...think "Excitebike" level creator taken to the extreme.