Use Vertex Painter for texturing? I'm trying to use Vertex paint to texturing my cube. But colors never show-up in the UVmap window or when export it !? 

I don't know where is my fault.
With Vertex Paint you are directly coloring model's mesh - so this technique doesn't use UV mapping to apply any kind of texture.

If you want to paint a texture (image), you need to switch to Texture Paint mode insted of Vertex Paint.