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- The images MUST be 1024x1024.
- The visible part of the image is 1024x768, in the top part of the image, the rest should be made black.
- Aplha values must be min. 1 and max 99. Only use integer values! (No decimals).
Have fun 
edit:
I made an example, using a wallpaper I found on internet.
The file containing gimp files, tga files and dds files can be downloaded from here