Click on the Apple button on the top left corner, and click "about this Mac".
A window with the specs of your Mac should appear.
For Windows
Type dxdiag in the search bar in the Windows menu and click dxdiag.
Click on the "Display" tab of the dxdiag window to see your graphics card information.
Fill in your PC information to see if it runs Dungeon Siege III
CPU
How do I know specs like this?
GPU
RAM
2GB
4GB
8GB
16GB
32GB
System
Windows
Linux
MacOS
Confirm
Requirements
Dungeon Siege III
Obsidian Entertainment
Minimum:
895
CPU: 
Core 2 Duo 2.5 GHz or equivalent
GPU: 
ATI Radeon HD 3870 or NVIDIA 9800 GT
RAM: 1.5 GB
OS: 
Windows XP SP3, Vista SP1, Windows 7
Recommended:
1138
CPU: 
Core i5 750 2.67 GHz or equivalent
GPU: 
ATI Radeon HD 4870 or NVIDIA GTX 260
RAM: 2.0 GB
OS: 
Windows 7
Homepage
Desktop Site
Fill out the specs below:
How do I know these specs?
CPU
GPU
RAM
2GB
4GB
8GB
16GB
32GB
System
Windows
Linux
MacOS
Confirm
Where do I find these specs?
For Mac
Click on the Apple button on the top left corner, and click "about this Mac".
A window with the specs of your Mac should appear.
For Windows
Type dxdiag in the search bar in the Windows menu and click dxdiag.
Click on the "Display" tab of the dxdiag window to see your graphics card information.