It's a true answer... An easy way to make a theme is to use another theme for reference. That way you'll now the name and size the images need to be and where they get placed in a theme.
nothing really "makes" themes. you cant just open up a program and hope its spits out something amazing that you can take credit for. you have to make the actual pictures theme itself with photoshop or gimp or something like that. the programs listed above just put it all together.
Actually not. You can create custom strings or even the info.plist easily with iDesigner. Themes are much more about finding what to change and the how to than creating images on photoshop... you can do a better theme than most around without any hard photoshop skill, just using google and finding the how to for everything you want to change.