Don't want KDE apps to appear in Gnome, vice versa

[VicAlpha]

How to do that?

[eniel]

Take a look at the following link:

http://ubuntu.wordpress.com/2006/01/13/ubuntu-to-kubuntu-keeping-the-menus-clean/

You can find the .desktop files in /usr/share/applications
and /usr/share/applications/kde

Those files determine amongst others how the application is shown in the menus. You can add the line
OnlyShowIn=GNOME;
or
OnlyShowIn=KDE;
to the desktop file.
Take a look at nautilus to see how this works:
sudo gedit /usr/share/applications/nautilus.desktop
(doubleclicking on the file will start nautilus)
you'll see a line OnlyShowIn=GNOME;