A Geoghegan Surname DNA Project has begun. Go to
www.familytreedna.com and search for Geoghegan.
You can order testing kits on-line. A 25 or 37 marker paternal y-chromosone kit is usually sufficient to begin.
To see a good example of the types of information and family group exchanges that can be achieved, go to
www.williams.genealogy.fm and see what this family has done.