Usually we take rumors lightly, but this one supposedly came from the Official PlayStation Magazine(UK?). A forum member at Killzone.com claims to have gotten his hands on the latest OPM- issue number 14 which contains some interesting snippets regarding Killzone 2.
Killzone 2 also promises the inclusion of player-controlled vehicles
Public beta test in mid `08
We asked deJonge to tell us a secret, As you know,they[Helghast] are not the only inhabitants. He wont be drawn on whether those other alien inhabitants are friendly or not.
This isnt from the North American OPM publication, as weve already gotten our hands on the latest issue. We want to know more and well let you know if theres any truth to this as soon as possible. Stay Tuned!
Source
I'll be getting this mag as usual on the 21st (when it's out), so hopefully I'll be able to confirm this.