Well done Nazgul!
About getting to play up a game, you'll find down from the snap shopt nazgul taken, written "forumla" you can choose prefrences, like what the rating you'd like to challenge for your oponent, rated game or not, ect....
after completing this step, you'll see down in the same area players seeking gamers with the time for the game, you simply double click on the username and play the game. Another option you could "search" just click on seek and choose the timings then users will click to play you.
About the serial number, you'll have like 3 months or less you can play for free and even get ranking , after that you'll be turned into a guest which you can pay but without "rating" or "chat" or "ranking" ect... but you could get a serial number its not very costly for 1 year from:
click here
My suggestion is to play for now until you be a guest, if you liked it
then get the serial number
and no you cannot get one from the web , i've tried :P