In the test version:

 Type in DISSENT as your name to get more stuff.  If you like hot babes
 then on the course Devil's Canyon right you go in a tunnel veer to the
 right quickly so u don't get put back on and there is girl in a bathing
 suit.

 Type in ABODE as your name to get all the bikes and to be able to drive
 on all possible tracks.

 In the full version type INSOMNIA to get the bike effect.

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 Open the file menudata.ini with a normal editor and look for the
 value

 Maxnumcompbikes

 and change that number to 0. Save and start the game and now you are
 alone on the tracks.