I followed the instructions on this postCustom World Maps and set all the options as instructed but when I select the map in the editor COTN crashes.
I made an an image 1024x768, resized the canvas to 1024x1024, making sure the image was centered at the top of the canvas, selected the blank (transparent) part of the image, inverted it and saved the selection to the alpha channel then saved it it in PSD format using PSP9.
Now, using the DDS plugin, convert your file to DDS format, with the following options:
-ARGB8888 (Alpha, Red, Green, Blue - 8 bits per channel)
-DXT3 Compression format
-Single MIP level
Below are the options I have set up for the conversion from the DDS Convertor.