Jason,
Whilst I'm not a native of Donegal, I have strong connections to that county. Firsly, I'd recommend that you read info from "Gael Saoire" here.
http://www.gaelsaoire.ie/asp/gaeltacht_home.asp?language=english&gaeltacht=Donegal Read the info they have on the website, and if you have questions I can answer, I'll gladly do so.
In the meantme, I'd say go to Glenveagh National park, in the shadow of Mount Eirigal. Fantastic views over Dunlewey lough. If you've got your walking boots with you, try climbing Errigal. The scenery around here is beautiful and very rugged.
Anyway, if you want more info,post and I'll try to help.