Motocross The Force
Full user review
"Great 'Retro' Game!"
Comes with a clever AI that learns as you play
Comes with a built in Screensaver!
Built In Track editor
The racing physics is pretty good too.
This is unfortunately the latest and last version of the game, it was never developed beyond this point and is no longer supported by the developers, although they do have a (commercial) Xbox version that was developed out of this.
This is a fun game that plays and feels a lot like Motorcross Madness 2 but free. The graphics are dated but is still quite playable.