Well for skinning I use (or used to use, I really suck at it) The GIMP. It's freeware and it's supposed to be just as good as Photoshop or Paintshop Pro.
I think when Darky says "Macintoch Modding Tool on the Site" he means ColorManager for Mac, ofcourse there's an PC version aswell. Check em out under the Tools section. I think they are simply the best color tool avaible out there. And yes, I'm brother to the creator if anyone asks.