Hello,
On Ubuntu 12.04 the serial port is greyed out when plugging in Nano v3. If I plug in a Uno this works fine and serial port (ttyACM0) is selectable.
The really odd thing is that if i plug the same Nano into my Ubuntu 10.04 setup the serial port selection is available (ttyUSB0) and on plugging in the same Uno a serial port for that is available too (ttyACM0). So my question is, as the Arduino boards are the same ones in each setup, why do they work ok in 10.04 but not the Nano in 12.04. I've tried both IDE 1.0 and 1.0.3 and get the same problem
On another note I have a similar issue in Windows 7. the Uno works fine but I am not able to install the driver for the FTDI so that the Nano can been seen. I've gone round in circles but I always end up with an error code 10 - can't start device. If I can solve the problem in Ubuntu 12.04 I'm not too fussed about getting it to work in Win7. Any help or pointers would be appreciated.