Hi,
try this:
Start up your computer
Open a console window
Run command "sudo dmesg -c" which prints and clears the kernel log messages since startup
Now plug the arduino board into an USB port
Run command "dmesg" in the console (no need to do this as root this time )
Post the output of the command it should look something like this
[ 1700.510090] usb 1-5.5: new full speed USB device using ehci_hcd and address 6
[ 1700.626476] usb 1-5.5: configuration #1 chosen from 1 choice
[ 1700.670375] usbcore: registered new interface driver usbserial
[ 1700.671013] USB Serial support registered for generic
[ 1700.671937] usbcore: registered new interface driver usbserial_generic
[ 1700.671941] usbserial: USB Serial Driver core
[ 1700.682074] USB Serial support registered for FTDI USB Serial Device
[ 1700.682788] ftdi_sio 1-5.5:1.0: FTDI USB Serial Device converter detected
[ 1700.682887] usb 1-5.5: Detected FT232RL
[ 1700.682891] usb 1-5.5: Number of endpoints 2
[ 1700.682894] usb 1-5.5: Endpoint 1 MaxPacketSize 64
[ 1700.682896] usb 1-5.5: Endpoint 2 MaxPacketSize 64
[ 1700.682899] usb 1-5.5: Setting MaxPacketSize 64
[ 1700.683228] usb 1-5.5: FTDI USB Serial Device converter now attached to ttyUSB0
[ 1700.683252] usbcore: registered new interface driver ftdi_sio
[ 1700.683255] ftdi_sio: v1.5.0:USB FTDI Serial Converters Driver
Eberhard