You'll need to have an Origin version of Spore to register normally. If you own a Steam version of Spore, you have to generate a CD key of the game by going to the Steam library, right-clicking on any Spore game, hovering over Manage, and clickking on "CD keys". I think you have to wait for it to generate for you.
For more into details, go to Steam Community :: Guide :: How to connect to Spore servers / link EA account (Steam and Physical)