After speeding too much time trying to find out what went wrong with the installation of a new module in python, I realised that the root of the problem is due to fault configuration of PyDev plug-in. On the contrary, the same module works fine in IDLE 3.2. So my question is: how could I configure PyDev with exactly the same settings as IDLE 3.2???
I don't know if you still have this problem, but I'll leave the answer anyway (just in case someone else comes across the same problem - like I did a few days ago).
From this tutorial: