I integrated SFML in a MFC window for my editor once. I guess that's what you are trying to do.
If using Qt window interface and SFML rendering is actually what you want, you must do something like this (its code using MFC, but i will do something similar in Qt)
m_RenderingContext = new sf::RenderWindow ();
sf::WindowHandle MyH = m_hWnd;// GetSafeHwnd();
m_RenderingContext->Create (MyH);
So basically I'm just getting window handle (which in this case is a part of my application window using to display OpenGL), and letting SFML initialize it just like a normal window.
//Edit: I thought i might add some more
Its actually implementation of the CChildView class of MFC, which should have its equivalent in Qt;
Also, i modified the OnPaint event to:
m_RenderingContext->Clear (sf::Color (0, 0, 0, 255));
/* Drawing code goes here */
m_RenderingContext->Display();