DotA 2 System Requirements for PC:

Operating System: Windows XP®, Windows 7®, Windows Vista®
Processor: Intel Dual Core 2.26 GHz or AMD Athlon equivalent
RAM: 1.0 GB Ram
Hard Disk: 5GB
Video Memory: Nvidia GeForce 8800 GT or Ati Radeon 3870 HD with 512MB memory.
DVD-Rom drive.
BroadBand Internet Connection.
Steam must be installed.
DirectX 9.0c
Keyboard
Mouse