Can I buy an expansion on Steam and use it with a retail game?

I own Spore, which I bought from Wal Mart when it was released. Steam is having a sale on Spore: Galactic Adventures, an expansion pack that requires the original game. If I bought the expansion on Steam, would it work with my regular copy of Spore? Or do I need to own Spore on Steam, as well?Can I buy an expansion on Steam and use it with a retail game?
I beleive you can register your retail copy of spore on steam. Then buy expansions.
you can add it at your steam libraryCan I buy an expansion on Steam and use it with a retail game?
I'm pretty sure you need the Steam version. Send an email to Steam to make sure
own spore on steam,Can I buy an expansion on Steam and use it with a retail game?
you need to own spore on steam, too