There's no program to "make them". It's just a matter of altering what's already there.
Take a look in your EverQuest directory. You'll see a dirctory called
uifiles. Inside there will be another one called
default.
Check out the files in there. That's the UI. All the files in there, the data, makes the UI.
You can use Notepad to alter the .xml files, and any graphic application that supports targa files for the .tga files.
Make sure you read over the .doc file first, then play with the files. Create a new directory in
uifiles and save any changed files (only) into that directory. That will be your new skin.
And be sure to do things like set Size X to 50 before posting "What does Size X do?".
Also, take note of the file
UIErrors.txt that's located in your everquest directory. If for any reason your UI doesn't load, the error will be in there. Even if EQ decided to take a nose dive on ya, cause it will, trust me, it will.
Post any questions you might have, but please make sure you read the docs and search the forums first. People are quite reluctant to post answers to question's that been asked too many times.
And, good luck to ya mate. Modifying the UI is really easy, don't get too intimidated. Just play with it and see for yourself.