According to this, you cannot write 100% Italian on a QWERTY keyboard but I am wondering how you would write Italian with a QWERTY keyboard then? For example, characters like ë, ï, and é are a huge pain since I currently have to keep opening Character Map, find the symbol, copy it, then switch windows and paste.
If you set your keyboard layout to us-international you can use the so called "dead"-keys.
You can use Shift+" followed by e to get ë.
Also Shift + ' / Shift + ^ / Shift + ` / Shift + ~ followed by the desired letter.
Way better then remembering those alt-combinations.
Keyboard layout is under configuration, keyboard an languages, change keyboard..under italy add us-international and set as default above in the pulldown. Choose apply and remove the other layout (presumably italian)¡ If you don't remove the italian you could accidentaly change back with shift+alt or some other combo.
You can use Alt codes. For example, for ë you would hold Alt and press numbers zero, two, three and then five in sequence (not at the same time), then release Alt. I believe you can use the top-row numbers, but I always used to use the Number Pad.
A full list is here: http://www.alt-codes.net