you know what I just did for you? I booted up into my old knoppix 3.3 hd install. Anyway, there are 2 (countem, two) Qtparted entries in the System submenu of Kmenu. I tried clicking on both in turn and both had the same result, throbby flashy, timeout whatever nothing happens. Not being one to stop at that I went into the kdmenu editor to see what they were pointing at and as whom:

1) qtparted = /usr/bin/X11/xterm /usr/sbin/qtparted
2) qtparted = sudo -H qtparted

Not helpful, so I ran in console as normal user self and inputted and the results:

1)nish@ecs:~$ /usr/bin/X11/xterm /usr/sbin/qtparted
/usr/bin/X11/xterm: bad command line option "/usr/sbin/qtparted"

usage: /usr/bin/X11/xterm [-/+132] [-C] [-Sccn] [-T string] [-/+ah] [-/+ai]
[-/+aw] [-b number] [-/+bc] [-bcf milliseconds] [-bcn milliseconds]
[-bd color] [-/+bdc] [-bg color] [-bw number] [-/+cb] [-cc classrange]
[-/+cjk_width] [-class string] [-/+cm] [-/+cn] [-cr color] [-/+cu] [-/+dc]
[-display displayname] [-e command args ...] [-fa pattern] [-fb fontname]
[-/+fbb] [-/+fbx] [-fg color] [-fi fontname] [-fn fontname] [-fs size]
[-fw fontname] [-fwb fontname] [-fx fontname] [%geom] [#geom]
[-geometry geom] [-hc color] [-help] [-/+hold] [-iconic] [-/+ie] [-/+im]
[-into windowId] [-/+j] [-/+k8] [-/+l] [-/+lc] [-lcc path] [-leftbar]
[-lf filename] [-/+ls] [-/+mb] [-mc milliseconds] [-/+mesg] [-ms color]
[-n string] [-name string] [-nb number] [-/+nul] [-/+pc] [-/+pob]
[-rightbar] [-/+rv] [-/+rvc] [-/+rw] [-/+s] [-/+samename] [-/+sb] [-/+sf]
[-/+si] [-/+sk] [-sl number] [-/+sm] [-/+sp] [-/+t] [-ti termid]
[-title string] [-tm string] [-tn name] [-/+u8] [-/+ulc] [-/+ut] [-/+vb]
[-version] [-/+wc] [-/+wf] [-xrm resourcestring] [-ziconbeep percent]
Type /usr/bin/X11/xterm -help for a full description.

yeah, even less helpful

2)sudo -H qtparted
nish@ecs:~$ sudo -H qtparted
nish is not in the sudoers file. This incident will be reported.
nish@ecs:~$

Still not helpful though it shocked me. I am (was) not a sudoer? But then again, I never sudoed after hd install, only su.

There IS (was) a known bug on a KDE version around 3.2.1with su. See two grave regressions: http://www.kde.org/info/3.2.2.php#binary. With that bug, you su something in the KDE menu and although in the dialog you input right password, it says wrong password...sounds like your prob. But, the fact is what you say works fine for you in knoppix 3.3 give the above results for me knpx 3.3. Maybe it is something like a security hole left by an inbetween update then closed afterward (in 3.4 knoppix and I think, it's 3.2.1 KDE)?

Anyway, what you are saying is dead-on about knoppix 3.4. But I think you had either customized or a hole on your 3.3 install...mine was the knoppix version 2.19.04. Maybe upgrade KDE what you can and see it it is fixed?