Blender: changing alpha transparency of an object via Python?

Question

I want to change the transparency of the aircraft in real time using the game engine. I found this script:

for x in [0,1,2,3]: own.meshes[0].getVertex(0,x).setRGBA([1,1,1,alpha_rate]) 

This works with materials without an attached image. However, now I added a UV texture to it and attached the image. The following code does not work. Is there a way to change the alpha of an object?

I am using Blender 2.49b with Python 2.5.1

Any ideas would be greatly appreciated.
Cheers
Will it