If you have Gnome installed, and from what you say, you have it. That means you already have the NetworkManager applet installed.
So the question should be, how to start it, in KDE.
Open a console and try this. 'nm-applet -sm-disable' without the quotes, just what is between them. That is the command that starts it in Gnome. All I did in Gnome, is looked at "Startup Applications" located NetworkManager, clicked it once, and selected edit.
Try that, and see if that works. I don't have KDE on my netbook, just Gnome, so I can not test it myself.