If the game it's original(bought throw Steam), you can't launch it that way.
i bought it through steam and it lets me launch it that way?
No, it doesn't let you launch that way, you will receive an error like ,,Steam must be running''.
No, you can run cod4 without steam even if it's bought over steam as it doesn't have a steam base, this does not mean that you will not get banned, as Punkbuster has nothing to do with steam.