You gotta have an early version of PS3 for being able to run PS2 games. Not sure which model, but chances are that you can't (the vast majority can't).
If there would be anyone online on Killzone I would be AMAZED. It was in the early days of online play and I never knew anyone that actually played online with PS2. It's a good game though, I played it this summer for the first time.
So yeah, you're on the KZ forums and nobody even replied regarding Killzone for 3 weeks so that's probably your answer regarding online acitivty. Or any activity 
