Official Homeland Defense: National Security Patrol system requirements
These are the PC specs advised by developers to run at minimal and recommended settings. Those requirements are usually very approximate, but still can be used to determine the indicative hardware tier you need to play the game.
Minimum system requirements
Recommended system requirements
Graphics card: DirectX® 9.0c compliant 64 MB video card and drivers (GeForce 2/ ATI 7000/ Intel GMA 900)