if you want to run fvwm with network-manger,
you can install stalone tray to run network-manager on fvwm,
#sudo apt-get install stalonetray
then from fvwm terminal run
#stalonetray --dockapp-mode simple &
and for network-manger run
#nm-applet &
you will get network manager
you can install stalone tray to run network-manager on fvwm,
#sudo apt-get install stalonetray
then from fvwm terminal run
#stalonetray --dockapp-mode simple &
and for network-manger run
#nm-applet &
you will get network manager