Ignore the error about vmwgfx. You don't need it. Once you have generated an xorg.conf file with 'Xorg -configure' you still have to modify it to enable both monitors. I suggest taking a look at:
http://www.thinkwiki.org/wiki/Xorg_RandR_1.2
http://wiki.debian.org/XStrikeForce/HowToRandR12
Basically, you'll edit your xorg.conf file to have two monitor sections, give them the identifiers that 'xrandr' uses, and set one of them to be to the left or right of the other.
Something like so:
Code:
Section "Monitor"
Identifier "DVI-0"
EndSection
Section "Monitor"
Identifier "DVI-1"
Option "RightOf" "DVI-0"
EndSection
Your Identifiers may be different, depending on the driver you are using (radeon vs. radeonhd) and the types of monitors involved.