In reply to Jonno: Jonno shut your shite spewing arse. Have you thoroughly explored every crag in Donegal? (I thought not). Have you traversed the lenght & breadth of Donegal? So coming out with these great catch all statements of yours is a bit prejorative of you, but then again i wouldn't expect any better from you.
To the OP: Easiest way to get to Donegal is probably to fly to Derry, Belfast or Dublin & rent a car from there. As another poster said you'll be able to get to Donegal (atleast the larger towns Donegal, killebegs, letterkenny) easily enough using public transport but getting around to crags & the like will be very hard & cause you alot of trouble.
The main crags are Malin Beg, Muckross Head, The Poisoned Glen & Gola Island. However the entire county is litered with crags small & large most of which are virtually untouched. For more info on routes check here:
http://www.climbing.ie/ & for bouldering check here:
http://www.theshortspan.com
Wild camping isn't a problem but at that time of year you'll be better off staying on the coast as the midges are little bastards & at scottish levels of nastiness at that time of year. One thing not to expect in Donegal is good weather not matter what time of year it is, but if you're lucky & the weather holds out it will be absolutely glorious. Oh & if the weather goes to shit you're likely to get be able to get some surfing in instead, as there is great surfing there too. Anyways hope it goes well & if you want or need anymore info drop me a mail through the site.