This document intend to describe how I managed to get a PC with :
two different monitors plugged to ...
two different graphic-cards, each matching ...
two different keyboards and mice
in order to run ...
two instances of XFree86, each one having it's own login screen, and thus having ...
two different users working on the same PC box at a time.
Such configurations are often called multiseat linux, multi-seat linux, multiuser X11, or some variations around
those themes.
Also, most of this setup can be used in order to produce more than two full featured independent X-servers :
users regularly reported 3 and sometime up to 5 or 6 seats, though in my opinion, it might lead to a bunch of wires.