I assume you use Linux here and the following applies to unix-like operating systems.
If you only want to use aMule, you don't need .po files. The translations are saved as .mo-files inside /usr/share/locale/it/LC_MESSAGES/amule.mo (possibly also in /usr/local/share/... or it_IT instead of it)
In order to use these files, you need to have this locale installed. Please check with the command locale -a in a terminal if your list contains "it_IT", "it" or similar. If not, please activate the locale by opening "/etc/locale.gen", removing the '#' character in front of the line saying "# it_IT.UTF-8 UTF-8" and afterwards running "locale-gen".
If the locale exists, aMule should show the translation. If not,please tell us what distribution you use and how you installed aMule.