So you want to make sprays with transparent backgrounds? It's pretty simple once you get the hang of it.
First of all, you need to install the Targa plugin for Photoshop (it is normal if you already have one,just install this one too). I've uploaded it
here. Read the readme to find out where/how to install it.
Then, make the picture you would like for your spray. You can work with shadows and everything you like. The parts you want to be transparent should only be left transparent for now.
When you are done developing your image, make a new layer at the top of the layer list. Select it, and press Ctrl+Alt+Shift+E. You notice that the 'image' of your creation is copied to that layer. At this point, you want to make sure that only that layer is visible (check off the eyes of the other layers).
As a next step, you want to select everything that is not transparent. An easy way to do this is holding down Ctrl and clicking on the top layer (the top layer with the image created by doing Ctrl+Alt+Shift+E).
Next, you move from the 'Layers' pallet to the 'Channels' pallet. There you see four 'layers' named channels. Leave them as they are, just press the 'Create new channel' button. You should see a 'black' picture with the selection of your image in it.
More to follow... gtg now