Hey,
how can i set the position and size of a texture which is rendered on a quad… ?
By assigning texture coordinates. http://www.rozengain.com/blog/2007/08/26/uv-coordinate-basics/ if you need to get a handle of the concept.
Also there are methods setScale and setTranslation in the jME Texture class (but they apply to the texture not a specific thing you put it on).