Convert a Texture into PolyPainting

From ZBrush Info

To convert a Texture into PolyPainting:

1. Load the Model
2. Load the Texture
3. Divide the model so that its polygon count is close to your texture's pixel count. If you don't want to learn the math behind this just divide it as far as you can. If you want to learn the math, here is some info: a 2k texture map has 4 million pixels in it. Your UVs only use 70% or less of that space so the pixel count is close to 3 million.
4. Press Tool: Texture: Txr>Clr

You're done.

To Learn About Baking PolyPainting into a Texture Map Click Here.