Finding a student job in Italy is not going to be as easy as some other international work searches. Italians can be a close knit bunch who tend to hire folks whom they know. In the case of searching for student work in Italy, you might be better off arriving with your backpack and getting to know some locals before you'll be able to land a job that isn't unpaid, like picking olives in return for a jar of olive oil (although that would be an adventure, you're looking for a job that actually pays).
Finding work on the internet before you go is said to be less than a snap. Prepare yourself when you do go with some guidebooks and maps, and brush up on your Italian... if you don't speak Italian, you may be out of luck finding a decent job in Italy.
That said, try these sources of information:
Casual job advice from backpackitaly.com
Jobs in Rome - some professional and some "non-skilled" job postings (secretarial, nannies, au pairs, possible hostel or bar and cafe work)
Italian work permits are very complex - unless you have a company sponsoring you, you may want to travel visa]look into declaring yourself to be self employed in order to work in Italy (as a translator, say) while you scope out the work scene and try to find an employer to sponsor you
The Facts - everything there is to know about Italy from About Guide Martha Bakerjian
Italian guide books
Bound Italian maps
"I am one of those who never knows the direction of my journey until I have almost arrived."
--Anna Louise Strong