or Windows 7 (SP1 recommended),
or Windows XP SP3
or Windows Vista SP1 (SP2 and Platform Update recommended)
800MHz processor (dual-core recommended)
512MB of RAM
1024 x 768 screen resolution
200+ MB hard drive space
Optional: 64-bit mode requires a 64-bit CPU and a 64-bit edition of Windows
Paint.NET does not work on Windows RT.
Paint.NET also depends on Microsoft's .NET Framework 3.5 SP1, which is automatically installed if it isn't already on the system.
Paint.NET uses your hard drive to store temporary files related to undo/redo history. Because of this, actual disk space requirements will depend on the actions you perform on an image, and on the size of the image.