In reply to Jonno:
I'm not exactly sure where Dunlewy is, but I'd say that you're looking at about 4 hours from Dublin to Donegal, maybe close to 5, depending on how far north you're going. If you're heading out on the N2 from the M50, then be sure to have a few euros change for the toll. If you're heading there through Northern Ireland, then fill-up with fuel in the Republic, if necessary, it's cheaper.