FUll Killing Floor system requirements

Minimum:
o OS: Windows 2000/XP/Vista
o Processor: 1.2 GHZ or Equivalent
o Memory: 512 MB RAM
o Graphics: 64 MB DX9 Compliant
o Hard Drive: 2 GB free hard drive space
o Sound: DX 8.1 Compatible Audio

Recommended:
o OS: Windows 2000/XP/Vista
o Processor: 2.4 GHZ or Equivalent
o Memory: 1 GB RAM
o Graphics: 128 MB DX9 Compliant with PS 2.0 support
o Hard Drive: 2 GB free hard drive space
o Sound: Eax Compatible

And incase you happen to like gaming on your Mac

Mac System Requirements

o OS: OS X version Leopard 10.5.8, Snow Leopard 10.6.3, or later.
o Processor: Intel Mac
o Graphics: Nvidia or ATI GPU (Intel GPUs unsupported)