I would like to be able to toggle between them using hot-key (single hotkey for toggle or hotkey for each display)
in windows it's very simple, but I couldn't find how to do it with nvidia-settings on my ubuntu 7.10.

# xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by failsafeDexconf, using
# values from the debconf database and some overrides to use vesa mode.
#
# You should use dexconf or another such tool for creating a "real" xorg.conf
# For example:
# sudo dpkg-reconfigure -phigh xserver-xorg