Hi, welcome to Subsim.
Have a look here -
http://www.subsim.com/radioroom/showthread.php?t=100366
I wrote this awhile ago and it may help you. The only thing I would add to this tutorial is that you don't need to repack and *.DAT files (if using GWX), just add them to the textures folder.
There are links to programs needed within the PDF/DOC. You will also need a graphics program/suite that can handle *.TGA file.
You can find all of Timtravellers tools here -
http://files.filefront.com/TimeTrave.../fileinfo.html
See how you go, however, I can give you a head start with JSGME arranged blank/default TGA files. Just create copies and work on them in their current locations. Type 7 & 9 files are available here:
IX -
http://files.filefront.com/IX+Textur.../fileinfo.html
VII -
http://files.filefront.com/VII+Textu.../fileinfo.html
Always looking for new skins, so please share anything you feel we would like to see.