Any tool ideas?

I'm about to undertake quite a large software project for my own interest which has a fairly complex backend as well as a very complicated user interface. It looks like there will be a lot of dialogues, or property inspector type pages involved also.

My primary target is to be Win32, although it would be nice to make it easily portable to other systems such as Linux. Due to the complicated backend it will be mainly written in C++, although I'd like to use as many free tools as possible, such as Dev-C++.

And so onto my question... From my experience with GUIs I know that they can be a real pig! They can take up a lot of programming time, and as this project is something that will be done in my limited spare time I can't spend too long on them. Do you know of any tools that can make life easier for handling the UI?

I'm thinking maybe wxWindows, although I've been to go straight for GTK+, although there seems to be only limited Win32 support.

I'm also very open to using a scripting language, such as Python, to handle the UI, and also to increase the customisability of the application.

If anyone could give me a few pointers it would be greatly appretiated.