The driver for the FTDI chip is part of the linux kernel and should just work. Your version of ubuntu should be recent enough. The files in /dev are created on-the-fly as soon as a new device is recognized.
Try this to check if your system recognizes the board:
sudo tail -f /var/log/messages
Then plug in the Arduino. You should see something very similar to this:
kernel: [ 4708.864051] usb 2-1: new full speed USB device using ohci_hcd and address 69
kernel: [ 4709.070077] usb 2-1: New USB device found, idVendor=0403, idProduct=6001
kernel: [ 4709.070116] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
kernel: [ 4709.070154] usb 2-1: Product: FT232R USB UART
kernel: [ 4709.070170] usb 2-1: Manufacturer: FTDI
kernel: [ 4709.070184] usb 2-1: SerialNumber: A6007nZC
kernel: [ 4709.070448] usb 2-1: configuration #1 chosen from 1 choice
kernel: [ 4709.195724] usbcore: registered new interface driver usbserial
kernel: [ 4709.195753] USB Serial support registered for generic
kernel: [ 4709.195786] usbcore: registered new interface driver usbserial_generic
kernel: [ 4709.195793] usbserial: USB Serial Driver core
kernel: [ 4709.236504] USB Serial support registered for FTDI USB Serial Device
kernel: [ 4709.236564] ftdi_sio 2-1:1.0: FTDI USB Serial Device converter detected
kernel: [ 4709.236594] usb 2-1: Detected FT232RL
kernel: [ 4709.236600] usb 2-1: Number of endpoints 2
kernel: [ 4709.236607] usb 2-1: Endpoint 1 MaxPacketSize 64
kernel: [ 4709.236612] usb 2-1: Endpoint 2 MaxPacketSize 64
kernel: [ 4709.236618] usb 2-1: Setting MaxPacketSize 64
kernel: [ 4709.238122] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB0
kernel: [ 4709.238238] usbcore: registered new interface driver ftdi_sio
kernel: [ 4709.238247] ftdi_sio: v1.5.0:USB FTDI Serial Converters Driver
BTW, does the green power light come on ? The yellow L-LED should also blink a few times after the board gets power from your computer.