I have been wanting to know this, i dont own a copy of COD 4i might end up buying a copy at some point though.
Yes, it'll play CoD4 fine - I've been playing through CoD:WaW on mine with the settings pretty much maxed out

Am I right in saying that these laptops have a spare HDD bay for an additional drive?
The 6930G does, but it requires a different bay cover to be purchased at ~£17 from Acer, the original default cover doesn't let you fit another drive in.