divide widescreen in 2 virtual

I've never heard of anyone dividing a single screen that way, but there are some ways to sort of simulate it.

The old-style dual screen setup creates two different displays, called :0.0 and :0.1. Each one is independent, and you can run a different window manager on each screen. This is often called "Zaphod mode".

The newer style puts both screens into a single, larger display. This allows you to drag windows from one monitor to the other, but requires special support from the window manager in order to work right.

But since you want two displays on one screen, neither of the usual setups will work. Instead, you'll have to either create virtual displays or use a window manager which can split the screen.

Virtual displays can let you keep using metacity, but accelerated video probably won't work, and you may have trouble getting some types of keypresses to go to the virtual display instead of the real one. However, it's not too hard to do. Try something like...

  % sudo apt-get install xserver-xephyr
  % Xephyr :3 -screen 960:1200 -ac &
  % Xephyr :4 -screen 960:1200 -ac &
  % DISPLAY=:3 gnome-session &
  % DISPLAY=:4 gnome-session &

That should produce two virtual displays, each running GNOME. But it's really not a great solution, and I don't recommend it as more than something to toy with.

A far more popular solution is to switch to a "tiling" window manager. This will let you divide your screen into non-overlapping sections, and run as many programs as you like in each section. But I must warn you, it's a little funky compared to a traditional window manager.

Some of the tiling window managers are "xmonad", "ion3", and "awesome". Or, if you really want to go minimalist, there's a rather mouse-unfriendly one called "ratpoison". You can install them with Synaptic, or "apt-get install xmonad" (for example).

I know this isn't exactly what you were asking for, but I hope it helps you find a solution.