X11 / xorg.conf file editing

I need to know if you edit this file for duel display monitors is there a way to extend from one to the other. My current config puts up two separate Desktops. so every time the screen saver loads it crashes my video card.
What do I need to edit. I can provide my VI file that I set if somebody can assist

Thanks

S.

I haven't done this myself, but this might be useful:

gentoo-wiki.com/HOWTO_Dual_Monitors#Configuring_X