The currency exchange rate used for ATM withdrawals is the wholesale rate and the rate used to convert funds for travelers checks is the retail rate. Check with your bank for information as to which system they are associated with (CIRRUS or PLUS, etc.) so you'll know which LOGO to look for at the ATM.
Ask at your bank about what charges are made on ATM cash withdrawals from European ATMs. Make sure you have a four digit NUMERICAL pin number. Test your card and have a back-up card with you if at all possible. Do take some cash as a back-up too (U.S. $ is best) which should be kept in a money belt under your clothes, along with your passport and your airline tickets, etc.
We were in Prague and Budapest in May and found that as everywhere else in Europe, the larger places accepted VISA and the Mom and Pop operations did not. This will not be a problem to you as long as you have your ATM card for obtaining cash. Before leaving home, make sure you leave enough as an available balance in your bank account.
By the way, VISA and MASTERCARD can be used to withdraw cash but if you're planning to do this, you should prepay your card and have a credit balance on it, so they won't be able to charge you interest on the cash you withdraw. But be advised, there are usually fees associated with cash withdrawals via credit cards.
Linda in Toronto