yes its possible, look at this one:
http://wn.com/6_Monitor_Linux_workstation_using_Ubuntu_and_Compiz
this guy use 6 monitors, so 3 its possible
now, here's a config i found : https://superuser.com/questions/132290/triple-monitor-setup-in-linux
# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings: version 1.0 (buildd@crested) Sun Feb 1 20:25:37 UTC 2009
# edited by me (brendan) 2010-04-18
# NVIDIA magic (something about glx-new?)
Section "Module"
Load "glx"
EndSection
Section "Extensions"
Option "Composite" "Enable"
EndSection
# Keyboards and Mice
Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
EndSection
Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection
# Physical Monitors:
Section "Monitor"
Identifier "Monitor0"
VendorName "Acer"
ModelName "Acer H233H"
HorizSync 40.0 - 70.0
VertRefresh 60.0
EndSection
Section "Monitor"
Identifier "Monitor1"
VendorName "Acer"
ModelName "Acer AL2216W"
HorizSync 40.0 - 70.0
VertRefresh 60.0
EndSection
Section "Monitor"
Identifier "Monitor2"
VendorName "BenQ"
ModelName "BenQ W500"
HorizSync 44.955 - 45.0
VertRefresh 59.94 - 60.0
EndSection
# Physical Video Cards/Ports:
Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 9800 GTX+"
# Screen 0
BusID "PCI:5:0:0"
EndSection
#Section "Device"
# Identifier "Device1"
# Driver "nvidia"
# VendorName "NVIDIA Corporation"
# BoardName "GeForce 9800 GTX+"
# BusID "PCI:5:0:0"
# Screen 1
#EndSection
Section "Device"
Identifier "Device2"
Driver "nvidia"
VendorName "nVidia Corporation"
BoardName "GeForce 7900 GT/GTO"
BusID "PCI:4:0:0"
Option "TVStandard" "HD720p"
EndSection
#### Default 3-monitor Layout 'default'
Section "ServerLayout"
Identifier "Default Layout"
Screen 0 "Screen0" 0 0
Screen 1 "Screen2" LeftOf "Screen0"
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
EndSection
Section "ServerFlags"
Option "Xinerama" "0"
EndSection
# Virtual Screens
Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24
Option "TwinView" "1"
# Option "NoTwinViewXineramaInfo"
Option "metamodes" "DFP-0: 1920x1080 +1680+0, DFP-1: 1680x1050 +0+30"
# Option "metamodes" "DFP-0: 1920x1080 +1680+0, DFP-1: 1680x1050 +0+15; DFP-0: NULL, DFP-1: 1680x1050 +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection
#Section "Screen"
# Identifier "Screen0"
# Device "Device0"
# Monitor "Monitor0"
# DefaultDepth 24
# Option "TwinView" "0"
# Option "metamodes" "1920x1080"
# SubSection "Display"
# Depth 24
# EndSubSection
#EndSection
#Section "Screen"
# Identifier "Screen1"
# Device "Device1"
# Monitor "Monitor1"
# DefaultDepth 24
# Option "TwinView" "0"
# Option "metamodes" "1680x1050"
# SubSection "Display"
# Depth 24
# EndSubSection
#EndSection
Section "Screen"
Identifier "Screen2"
Device "Device2"
Monitor "Monitor2"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "1280x720"
SubSection "Display"
Depth 24
EndSubSection
EndSection
Of course you will have to modify it but that will help you to see how ti works
found another tread about it: http://ubuntuforums.org/showthread.php?t=1502753
another one: http://ubuntuforums.org/showthread.php?t=1811366