Bene! Non aggiungo altro... 
You can get it from our download page, http://www.eecs.wsu.edu/paint.net/download.html
Or, if you already have v2.5 installed, you can get it through the built-in updater. First make sure that the menu item "File -> Updates -> Also check for Betas" is enabled. Then click the "File -> Updates -> Check Now ..." menu item. Don't worry if you don't have .NET 2.0 installed -- it will be downloaded and installed automatically if necessary.
Here's what's new:
- Now uses .NET Framework 2.0
- Full support for 64-bit processors, both x64 and
Itanium (32-bit also supported, of course)
- UI has been aesthetically upgraded (new icons,
toolbars, etc.)
- Layer ordering has been flipped "right side up" in
the UI
- Layer composition engine is now correct, and also
much faster
- Seven new layer blend modes: Color Burn, Color
Dodge, Reflect, Glow, Overlay, Negation, and Xor
- Checkerboard "transparency" background is now
rendered in screen coordinates so that it does not scale with the zoom level
- Pixelate effect is now much faster
- Ability to choose language during setup
If you have a 64-bit processor and are running a 64-bit edition of Windows, I think you will really like this release. Performance in 64-bit mode is greatly enhanced in many areas, including a 300% boost to the Gaussian Blur effect.
Oh and when I say "full 64-bit support," I'm not
joking. That means both x64 and IA64 
Fonte: Paint.NET v2.6 Alpha 1 now available: .NET 2.0 and full 64-bit support!