Ok, the answer is in this thread:
http://forums.eagle.ru/showthread.php?t=34693&highlight=serial+number
No offense ED, but this is ridiculous. It shouldn't be this complicated to install a piece of software.
Either update your pdf's, or put this info somewhere really obvious like on the home page. I shouldn't have to seach all over the forums (after registering again, once to buy the game then again to join the forums) to find a vital piece of info that is totally contradicted in the installation instructions.