Now I know I got this to work before but right now I can't work out how to do it. I have been reading the tutorials and I have the 'edit base textue' one open in front of me. I know how to change the alpha shape but there's a problem. The alpha layer is not workeable, even a new layer on top pof it won't take colour from the paintbrush. I'm using PS CS3. How do I set the alpha layer so that I can work on it? It doesn't say anything anywhere about this in goolge either, why are my alphas unchangeable, even with a new layer on top? What am I doing wrong?

The alpha is not a layer, but a channel. Windows > Channels and you'll see RGB, R, G, B, and Alpha. Select the alpha channel only, as if it were a layer. Now you can paint on it with white, black, or grey.

Personally, I find it easiest to make my textures normally, with whatever I want set to white on the alpha separate from any background. Then, once I get everything set up exactly the way I want it, I duplicate the layer bits I want white on my alpha, combine them, lock the transparency, and dump them full of white. Then put a new layer behind it and dump it full of black. CTRL-SHIFT-C to copy combined, and then switch to the alpha channel and paste the result into it.

You do need to have your image flattened before saving as a DDS too, so I tend to work in a new document rather than the same one - that is, paste the alpha into the alpha channel of a new document, set up my textures in one and copy them and paste them into the RGB of a new document... just easier that way, though you can do it all in one - just make sure to save a layer-separated copy first.

Thanks HP, the problem is, when I copy and paste to another layer the alpha eems to disappear and I'm just left with the texture. I'm trying to mess with objects here, just playing around a bit.

I wanted to put a layer over it so I can see where I'm cutting the alpha but it just won't work.

I'll need to keep playing with it and write down whatever works for me. I don't understand why it won't do for me what it does for everyone else, I'm obviously making some stupid mistake.

If I try to paint with black on the alpha itself, it tells me the area can't be transformed

Actually it says the target channels are hidden if I switch off the rgb to work on the alpha