Although the rate will be much better than what you could get by exchanging cash, I believe that ATM transactions are subject to a 1% foreign exchange fee (The samed one charged by Visa and Mastercard for purchases).

I've never been charged a fee by an ATM machine abroad, however, my bank does charge $1.50 per transaction, so an earlier poster's advice to find a foreign bank ATM part of your home bank's network is well taken.