+1  A: 

Subclass QProgressBar, add the dot to the class as a QLabel, then use setPixmap() on the QLabel. You will need to overload the paintEvent() for your widget to move the dot to the right position.

PiedPiper
What about displaying the whole thing as a continous thingy? Like a line ...
Geo
You could use a QFrame to draw the line
PiedPiper