- Install the twm package:
sudo apt-get install twm
- Create a twm desktop config file for your display manager:
cat > /usr/share/xsessions/twm.desktop
Now, you're free to select twm from the list of display managers. I really ought to get around to submitting a mod to the twm package as this config file should be in the distribution automatically, like the other window managers are.
And yes, I use TWM every day on my quad display system. It's the best, fastest, and least intrusive window manager I've ever used.