Quake3World

Is it possible to, in anyway, call the alpha channel of a tga, to use as a texture stage. As an example, I would like to use the alpha of a lamp as the "glow" stage in the shader... Or, use that alpha as the glow for a totally different lamp, not the same. Hope you understand what I mean.

You can't. The alpha channel isn't stored separately inside the engine, it's all RGBA data.