Corrigir lista de fontes.
Ir para /etc/apt/
Execute gedit sources.list
e cole o seguinte nesse arquivo:
# deb cdrom:[Debian GNU/Linux 7.0 _Kali_ - Official Snapshot amd64 LIVE/INSTALL Binary 20130315-11:02]/ kali contrib main non-free
# deb cdrom:[Debian GNU/Linux 7.0 _Kali_ - Official Snapshot amd64 LIVE/INSTALL Binary 20130315-11:02]/ kali contrib main non-free
deb http://http.kali.org/kali kali main non-free contrib
deb-src http://http.kali.org/kali kali main non-free contrib
## Security updates
deb http://security.kali.org/kali-security kali/updates main contrib non-free
deb-src http://security.kali.org/kali-security kali/updates main contrib non-free
Executar sudo apt-get update
E agora execute:
sudo apt-get install kali-defaults kali-root-login desktop-base kde-plasma-desktop
O KDE será instalado no Kali Linux