hey guys, I've been using three monitors with two nvidia cards for years with gnome, kde, ratpoison, awesome, etc. the only trouble I have is now that I'm trying out xfce, it doesn't see the third monitor because xfce relies on xrandr which is not what the proprietary nvidia driver uses.

here's my xorg.conf, I hope this helps.

Code:
# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 1.0  (buildd@palmer)  Fri Apr  9 10:35:18 UTC 2010
# commented out by update-manager, HAL is now used and auto-detects devices
# Keyboard settings are now read from /etc/default/console-setup
#Section "InputDevice"
#	Identifier     "Keyboard0"
#	Driver         "keyboard"
#EndSection
# commented out by update-manager, HAL is now used and auto-detects devices
# Keyboard settings are now read from /etc/default/console-setup
#Section "InputDevice"
#	Identifier     "Mouse0"
#	Driver         "mouse"
#	Option         "Protocol" "auto"
#	Option         "Device" "/dev/psaux"
#	Option         "Emulate3Buttons" "no"
#	Option         "ZAxisMapping" "4 5"
#	# generated from default
#EndSection

Section "Files"
	FontPath        "/usr/share/fonts/X11/misc"
	FontPath        "/usr/share/fonts/X11/100dpi/:unscaled"
	FontPath        "/usr/share/fonts/X11/75dpi/:unscaled"
	FontPath        "/usr/share/fonts/X11/Type1"
	FontPath        "/usr/share/fonts/X11/100dpi"
	FontPath        "/usr/share/fonts/X11/75dpi"
	FontPath        "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
	#RgbPath         "/usr/X11R6/lib/X11/rgb"
	# path to defoma fonts
EndSection

Section "Monitor"
	Identifier     "Monitor0"
	VendorName     "Unknown"
	ModelName      "HP LP2065"
	DisplaySize     408    306
	HorizSync       30.0 - 92.0
	VertRefresh     48.0 - 85.0
	Option         "CalcAlgorithm" "XServerPool"
	Option         "DPMS"
EndSection

Section "Monitor"
	Identifier     "Monitor1"
	VendorName     "Unknown"
	ModelName      "HP LP2065"
	DisplaySize     410    310
	HorizSync       30.0 - 92.0
	VertRefresh     48.0 - 85.0
	Option         "CalcAlgorithm" "XServerPool"
EndSection

Section "Monitor"
	Identifier     "Monitor2"
	VendorName     "HWP"
	ModelName      "HP LP2065"
	DisplaySize     410    310
	HorizSync       30.0 - 92.0
	VertRefresh     43.0 - 85.0
	Option         "CalcAlgorithm" "XServerPool"
EndSection

Section "Screen"
	Identifier     "Screen0"
	Device         "Device0"
	Monitor        "Monitor0"
	Option         "AddARGBGLXVisuals" "True"
	Option         "NoLogo" "True"
	Option         "TwinView" "1"
	Option         "TwinViewXineramaInfoOrder" "DFP-0"
	Option         "metamodes" "DFP-0: nvidia-auto-select +0+0, DFP-1: nvidia-auto-select +1600+0"
	DefaultDepth	24
	# Removed Option "TwinView" "0"
	# Removed Option "metamodes" "DFP: nvidia-auto-select +0+0"
	SubSection "Display"
		Depth       24
	EndSubSection
EndSection

Section "Screen"
	Identifier     "Screen1"
	Device         "Device1"
	Monitor        "Monitor1"
	DefaultDepth    24
	Option         "AddARGBGLXVisuals" "True"
	Option         "NoLogo" "True"
	Option         "TwinView" "0"
	Option         "metamodes" "nvidia-auto-select +0+0"
	SubSection "Display"
		Depth       24
	EndSubSection
EndSection

Section "Screen"
	Identifier     "Screen2"
	Device         "Device2"
	Monitor        "Monitor2"
	DefaultDepth    24
	Option         "TwinView" "0"
	Option         "metamodes" "DFP: nvidia-auto-select +0+0"
	Option         "AddARGBGLXVisuals" "True"
	Option         "NoLogo" "True"
	SubSection "Display"
		Depth       24
	EndSubSection
EndSection

Section "Module"
	Load           "dbe"
	Load           "extmod"
	Load           "type1"
	Load           "freetype"
	Load	"glx"
EndSection

Section "Extensions"
	Option         "Composite" "Enable"
EndSection

Section "ServerLayout"
	Identifier     "Layout0"
	Screen      0  "Screen0" 0 0
	Screen      1  "Screen1" RightOf "Screen0"
	Option         "Xinerama" "1"
	Option         "AIGLX" "true"
	Option         "RenderAccel" "true"
	Option         "AllowGLXWithComposite" "true"
	Option         "XGL" "true"
	# commented out by update-manager, HAL is now used and auto-detects devices
	# Keyboard settings are now read from /etc/default/console-setup
	#	InputDevice    "Keyboard0" "CoreKeyboard"
	# commented out by update-manager, HAL is now used and auto-detects devices
	# Keyboard settings are now read from /etc/default/console-setup
	#	InputDevice    "Mouse0" "CorePointer"
	#Screen      0  "Screen0" 1680 0
	#Screen      2  "Screen2" RightOf "Screen1"
	# Removed Option "Xinerama" "1"
	#Screen      1  "Screen1" LeftOf "Screen0"
EndSection

Section "Device"
	Identifier     "Device0"
	VendorName     "NVIDIA Corporation"
	BoardName      "GeForce 7300 GT"
	BusID          "PCI:1:0:0"
	Driver	"nvidia"
	Option	"NoLogo"	"True"
EndSection

Section "Device"
	Identifier     "Device1"
	VendorName     "NVIDIA Corporation"
	BoardName      "GeForce 7300 GT"
	BusID          "PCI:16:0:0"
	Driver	"nvidia"
	Option	"NoLogo"	"True"
EndSection

Section "Device"
	Identifier     "Device2"
	Driver         "nvidia"
	VendorName     "NVIDIA Corporation"
	BoardName      "GeForce 7300 GT"
	Option         "NoLogo" "True"
	BusID          "PCI:16:0:0"
	Screen          1
EndSection