I know that this question has already been answered but I can't remember nor can I find it.
How do you create a GCT file and what are the tools needed?
You need to import your .txt file into Code Manager, then export it as a GCT.
I found the more detailed instructions and I had Code Manager from when I downloaded it a long time ago.
You could use GCTedit (http://www.mediafire.com/?my2iuknzz0y) as well, it only needs the GCT file.