There's a step-by-step in Scarlet-Left's reply, I'd suggest you try that, particularly as it will guarantee that the folder structure is correct.
If you don't see the picture pack available as an option to select from Database Details then that means one of a handful of things:
1 - You've given it an invalid name (e.g. the folder name has too many characters in it)
2 - It doesn't have the correct folder structure (again, you can check it against the Default picture folder to see if it's correct)
3 - It's not in the correct place (again, simply check it against the Default picture folder - it should be right next to it and not be "double-foldered" inside)
Those are the only three reasons it won't appear, so you should be able to work out which it is just by careful examination of your TEW folders. Number three is the most likely, 9 times out of 10 it's because the user has double-foldered it, as I explained in my original reply. If you follow the instructions indicated in Scarlet's post you avoid these issues though, as the game will create the folders for you and you can simply paste everything into the correct spots.