While I absolutely love PyLNP, there is one thing that's been bugging me for a while now: the user interface. It looks a bit cramped, and the tabs (although they are kind of logically grouped) contain lots of settings. Especially the graphics tab took me a while to understand. Also, the original LNP's way of displaying and changing setting values doesn't really look like a proper Windows/Mac/Linux GUI. A lot of settings could be displayed using checkboxes, comboboxes and textboxes in stead of buttons.
Anyways, the last few weeks I've been trying to build a new GUI for PyLNP which is more focused towards the two most important features (at least to me): Launching Dwarf Fortress and launching utilities. Furthermore, my goal was to make it look more like a proper Windows/Mac/Linux GUI.
For this GUI, I've created a fork of Pidgeot's python-lnp Bitbucket repository and created a new GUI on top of the core modules that he already built, using PyQt4. Hence, everything that is in the GUI should actually work correctly (no guarantees though ).
It certainly does look nice. I don't entirely know about the use of a separate window for settings (especially a modal window), but it seems it shouldn't be too hard to e.g. move it to a tab or something.
As far as I can tell from a quick scan of the screenshots, the missing features (compared to the current source code) are the defaults button, folder opening, pack simplification, and the entire mods interface.
I'm not a fan of the way you're handling downloads - since the action needs to be retried, I don't think the download status window should be modal. Perhaps that's another thing you want to revisit later, if so, that's fine.
I notice the UI seems to crash for some older versions; 34.11 works, but 31.01 doesn't. There's no error output, and I haven't dug down far enough to know exactly why (but my guess is that you're not handling the differences between legacy and SDL builds).
FYI: If you think you will eventually want to submit a pull request with your changes, remember that the code should strive to support both Python 2 and 3. You should import unicode_literals and print_function from __future__ to help with this.