where is the alpha butten so the black uv becomes transperant?
in blender 2.5

Im not sure what button you are talking about. you know where it was in 2.49 ? UV face? You can assign a material to the face in the material window and there add alpha .
Hope that helps ya a little.

within the texture buttons, open the ‘image sampling’ tab, and under ‘alpha’ click ‘calculate’.