This is an April's fools joke, right?
There's no download there, just a 404.
Damn, I have to do things right for you, always! :P
most of the mirrors I found are down, the dev's page has no link to it (public, it's hidden), so ...
Here is the only mirror that worked that I founf.
This is the direct link to the ROM:
http://www.worldofguert.com/MotocrossChallenge_ROM.zip
Enjoy now