You have to make your own scene node, to begin with.(Actually it's possible without scene node, but that's a different story)
The scene node should have four verticles, which make up two triangles. Those verticles have what is commonly called UV-coordinates, check this site for more info about them (
http://nexe.gamedev.net/directKnowledge ... oordinates). Alternatively, google for "Texture coordinates".
You have to modify the UV-coords to display the area you want.
Basically its (1/Pixels)*PixelNumber to get the coord at a given pixel. (Both for x and y)
If you don't have anything nice to say, don't say anything at all.