Check if Qwt has one or find a "volunteer" to implement one.
Just had a quick look: Qwt has extra sliders, but no such "range slider".
Qt Labs has recently released a demo for embedded devices, which includes code for a QtMultiSlider, maybe we can borrow the code from there:
Also, there is another extension pack for Qt, the Qt eXtension library" Qxt (available in version 0.5):
They also offer a range slider, called "QxtSpanSlider". Couldn't find a screenshot though.
with your okay I would add qxt to the public MITK's utilities.
It is a Qt extension which adds some nice new widgets, like the 2 value slider.
Also offers some improved Qt widgets, e.g. buttons with rich text support or improved lists.
Michi, some of these could be interesting for data manager.
After file cleanup it has now only 580 kB.