Yeah, the big issue is getting Wifi access. What APs there are in Italy are locked down. (I see Alice APs all over town, but they're probably residential). If you're going to a hotel with Wifi, make sure they really do have wifi, and don't just claim it.

The way SIM cards work in Italy is:
A. You go to a retailer (rivenditore) specializing in cellphones.
B. You ask to buy so-and-so a prepaid card.
C. They make you fill out a form, including your residence in Italy (use your hotel)
D. They photocopy your passport.
E. You pay them.
F. They tell you they will "Fax in the forms tonight at 7:30" and you should see activation shortly after that.
G. You come back the next morning, and make them fax the forms in. Be aggressive. This is called rompere le scatole (well, it's called something else, but this is a family board), and it's how things get done in Italy. Experts will point out that you can skip the "next morning" bit and start breaking balls immediately, and get better results. Foreigners, however, should be circumspect in adopting unfamiliar local customs.
H. Service is activated shortly thereafter.

Oh, and you'll want to make sure your phone can work on European GSM networks. (tri-band at least)


So, in short, the N800 will be just as effective as a laptop for your trip.

You'll want to load up the region on Maemo-Mapper before you go.