In order for you to play Alien Swarm on Windows with minimal graphics settings, your computer must meet the following requirements
OS *:
Windows® 7 / Vista / Vista64 / XP
Processor (CPU):
Pentium 4 3.0GHz
Memory (RAM):
1 GB for XP / 2GB for Vista
Graphics Card:
DirectX 9 compatible video card with 128 MB, Shader model 2.0. ATI X800, NVidia 6600 or better
Hard Drive:
At least 2.5 GB of free space
Sound:
DirectX 9.0c compatible sound card
In order to play Alien Swarm on Windows with maximum graphics settings, you need a computer with a configuration no worse than the following
OS *:
Windows® 7 / Vista / Vista64 / XP
Processor (CPU):
Intel core 2 duo 2.4GHz
Memory (RAM):
1 GB for XP / 2GB for Vista
Graphics Card:
DirectX 9 compatible video card with Shader model 3.0. NVidia 7600, ATI X1600 or better
Hard Drive:
At least 2.5 GB of free space
Sound:
DirectX 9.0c compatible sound card