I looked at KDE SVN and revision 966608 promises "Support connecting to hidden wireless networks". I haven't tested it yet because I don't have any hidden network but someone may give it a try. Kubuntu experimental PPA (http://ppa.launchpad.net/kubuntu-experimental/ubuntu) plasma-widget-network-manager has been updated to newer revision 966653 so you don't need to compile.
I looked at KDE SVN and revision 966608 promises "Support connecting to hidden wireless networks". I haven't tested it yet because I don't have any hidden network but someone may give it a try. Kubuntu experimental PPA (http:// ppa.launchpad. net/kubuntu- experimental/ ubuntu) plasma- widget- network- manager has been updated to newer revision 966653 so you don't need to compile.