Both GTK+ and Qt have bindings for all popular languages. If you stick to
Pascal:
http://www.freepascal.org/packages/gtk.html
http://wiki.freepascal.org/Qt_Interface
However, it may be a good idea to learn a more modern and, today, more
popular language such as Python, which follows as well the object-oriented
paradigm. Here are the bindings of GTK+ and Qt for Python:
https://wiki.gnome.org/Projects/PyGObject
http://www.riverbankcomputing.com/software/pyqt/
As for the IDE, I don't use any (Emacs rocks) but, as far as I understand,
Eclipse remains the most popular. Whatever the language. Even Pascal:
http://sourceforge.net/projects/pascaline/
And, really, you should not use any graphical tool to create GUI. The code
that is produced is terrible (with absolute coordinates and so on) and not
portable. You need to learn about "layouts".
