buy it via Steam or DVD Rom?

[Anvilfolk]

I'm not sure and haven't installed myself, but it seems that CoD will always have to be associated with a Steam account, and use Steam itself.

I must I've used steam for almost as long as it's existed and never had problems. I personally love it - the only gripe I have with it is that you cannot install games to wherever you want. They go in the steam folder, so make sure to install steam to where you want your games to be!