Just got my CA license plate this is how i did it.
http://www.dmv.ca.gov/forms/reg/reg230.pdf
print out form 230 from DMV website under Vin I put teh vin # of my bike then to make the vin 17 #s like a car i put the name of my bike to fill in the rest so i looked like CRANBR###########. I have a Huffy Cranbrooke.
Engine # i just put the spark plug product #
Make was HUFFY
Fill out the rest and mail in with $19. ( this was in 2009)
Wait 3 weeks and you get it.
My registration papers says it is a motorized bicycle but under body type it has the code MP (moped?) and says it is a moped under type vehicle use.
heard it can take a few tries
Good Luck