Thanks Mike. This is the "original" light polluted version (scaled down):
http://piggo.com/~troy/photos/2009/2...tauri_orig.jpg
This is the best I could do with colour. I picked the colour of the background light pollution and painted that in a new layer and set the layer mode to "subtract". All the stars came out blue/cyan and the core was too dark. So I created a layer mask using a grayscale of the original shot, played with the contrast of the layer mask and got this. Result is that the bg LP is gone, but the stars have that vomit colour hue.
http://piggo.com/~troy/photos/2009/2...uri_masked.jpg