Not sure what you're exactly trying to do, if you already got it or whatever, but I think I can drop some general PS skinning thoughts here since it's already getting a bit OT
1. I start with a 320*213 image (File -> New)
2. Open the image you want as background image
3. Copy it into the 320*213 image
4. Resize/Position with Strg+T (Free Transforming)
Then add windows/style etc in the 320*213 image.
Just my 2 cents.
BTW I'm working with PS CS3. Those steps should work with all PS versions, and also GIMP I think.
PS: This is just how I'm handling Landscape only skins... Vox ones are a bit more complex, but I guess you don't mind about that :D