You should follow the Tobias suggestion, having a solid C++ background is pretty useful when learning Qt.
Probably you already know it but, the "Thinking in C++":http://www.mindview.net/Books/TICPP/ThinkingInCPP2e.html is a great book that you can get download for free.
Anyway the Qt Object Model is a subject on its own, that needs its own explanation, a nice one (with pretty figures :D), is in the L2 "Presentation with notes" of the "Qt Learning material":http://qt.nokia.com/services-partners/qt-in-education/qt-in-education-course-material, altough this material is intended to be used for teaching Qt I think it's clear enough even for the beginners.
And if you're looking for more detailed explanations check the "Qt eLearning videos":http://qt.nokia.com/developer/learning/elearning, specially the "Qt Training modules":http://qt.nokia.com/developer/learning/online/training/modules your question is answered in the "Objects int Qt" ones.
Happy learning!