CPU: I5-2500k @ 3.3ghz
RAM: Corsair Vengance 8GB @ 1600mhz
MB: MSI-P67A-GD65
GFX: Asus/XFX HD6950 2GB
cheap 850 psu.
but in all honesty i turn half the settings down for better performance rather than eye candy and my monitor is quite a cheap one and it only supports a fixed res of 1400x900 so i can't even use my card to it's full advantage.
The problem with yours kk must be the dual core ya gfx card is capable of running it your cpu came out in 2006..it obviously can't process the ai, actual zombie count, ambient spawns, loot spawns all at the same time, mixed with players on server, this is why dice refrain from more than 24 players on console, just not gunna keep up.
on top of this xp wants a gig of your 2 gig memory.. so..
you know it must be cpu related because when ya in mission editor with no ai it will work 100%.
I know it sounds much but you can upgrade now for about 300 quid from what you have and get a decent up-tp-date cpu and motherboard/ram and be able to play any game on pc, not just this..then a few months down the line get yaself a nice gfx card which most new ones will be able to run any game you throw at it.
If you do, it would be nice to play some pc games, you would enjoy it much much more, the ps3 is GREAT but also limited in many ways.
If you buy a cpu/motherboard and ram for about 300 and then in a few months upgrade ya gfx (160 quid), you won't be far off a pc nerd with superior gfx, LOL.
Then you can join in the pc elitism and become a gaming god and talk down to peasants on consoles

lol, just kidding, don't become one of them please hehe.