In order for you to play Alien Swarm: Reactive Drop on Windows with minimal graphics settings, your computer must meet the following requirements
OS *:
Windows® XP or above
Processor (CPU):
Pentium 4 or newer
Memory (RAM):
2 GB RAM
Graphics Card:
DirectX 9 compatible video card with 128 MB, Shader model 2.0b. ATI X800, NVidia 6600 or better
DirectX:
Version 9.0b
Storage:
7 GB available space
Sound Card:
DirectX 9.0c compatible sound card