If you're running KDE then make a shortcut pointing to
Code:
kdesu ifconfig eth0 down
Use your own network interface eth0 eth1 etc.
KDE will prompt you for a root password.
You can make another one for
Code:
kdesu ifconfig eth0 up
Or if you want to auto launch a terminal then something like
Code:
aterm -e sudo ifconfig eth0 down
Or Xterm