Im pretty sure its possible, but how would you alpha map a texture so that the alpha is in a gradient and not just a cut off straight line?
something like in the attatched image, where the green is alpha/transparent (i know its nomally black, but i made it green so its easy to see)
You may have forgotten to attach the image. You can create alpha gradients in many 2D graphics programs. Probably the most flexible of the free ones is Inkscape.
oh right, nevermind, i think my blender was broken, its working now in 2.53