Hi Richard.
Yes, you will be able to exchange US currency to Euro in Ireland including $100 bills. You will also get a better rate in the City Centre than you would in the Airport. Be careful reading online, a lot of people advise using a bank rather than a bureau de change, but many will not unless you have an account with the bank. ATMs can also be convenient and give you the best rate.
Let me know if you have any other questions.
Cathaoir