class Application(QDesktopWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self)
        ....

    app = QtGui.QApplication(sys.argv)
    myapp = Application()
    myapp.show()
    
    sys.exit(app.exec_()

class ShowIpDialog(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = IpDialogClass()
        self.ui.setupUi(self)

        _ipDialog = ShowIpDialog(parent=self)
        _ipDialog.show()
        _ipDialog.move(50, 50)
        _ipDialog.setFocus()