In order for you to play Steam Tactics on Windows with minimal graphics settings, your computer must meet the following requirements
OS *:
Windows 7 or higher recommended, though even Windows XP SP2+ should work
Processor (CPU):
Intel Core2 Duo, equivalent or better
Memory (RAM):
2 GB RAM
Graphics Card:
DX9 (shader model 3.0) or DX11 with feature level 9.3 capabilities
Storage:
100 MB available space
Sound Card:
Any