Originally Posted by JDR13 
I see this is actually a trial version. Do they really expect people to pay $20 for a 19 year old game?
It's free now but apparently the in-game text was never changed to say that. The
official website has the registration info you need to unlock it in a PDF. It's kind of fiddly though - first you have to reset it to enter in the matching serial number. After the serial number is reset you can enter the registration code.