You could mix the GTK (Gnome) and the Qt (KDE) based applications. With the KDE/Kubuntu desktop the Gnome applications will install the needed GTK libraries.
Here with the Kubuntu 11.10 (simulation):
:~$ sudo apt-get -s install planner
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
gconf2 gconf2-common libart-2.0-2 libgconf2-4 libglade2-0
libgnomecanvas2-0 libgnomecanvas2-common libgtk-3-0 libgtk-3-bin
libgtk-3-common librarian0 rarian-compat scrollkeeper
gconf-defaults-service librsvg2-common gvfs
The following NEW packages will be installed:
gconf2 gconf2-common libart-2.0-2
libgconf2-4 libglade2-0 libgnomecanvas2-0 libgnomecanvas2-common
libgtk-3-0 libgtk-3-bin libgtk-3-common librarian0 planner
--- EDIT ----
Well - that was a simulation ; )
s, --simulate, --just-print, --dry-run, --recon, --no-act
No action; perform a simulation of events that would occur but do not actually
change the system.
Installing with the command
sudo apt-get install planner
Trying to start the Planner
K > Applications > Office > Project Management
There seems to be problems. Starting from the konsole the planner is giving an error message:
The program 'planner' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAccess (attempt to access private resource denied)'.
(Details: serial 764 error_code 10 request_code 152 minor_code 1)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)
Turning the Desktop effects off (Alt+Shift+F12). System Settings > Desktop Effects.
A bit better. The Planner is starting but the planner window is blank.
Turning the Desktop effects on and turning the GTK widget style to the Raleigh. System Settings > Application Appearance > GTK+ Appearance.
Now the Planner is starting and the planner window is readable.
--- EDIT #2----
The KDE project planner app is the KPlato: http://www.kde.org/applications/office/kplato/. I can't say what it's status is (good/bad). Package is kplato.