For riding places, depends upon where you live--the state website lists state forests and parks where ATVs may be ridden legally--Green Ridge State Forest (near Cumberland) is one. Southern Maryland ATV Park just opened near Bud's Creek; south of La Plata. Call 'em; they may have rental quads.
PAAtving.com lists PA riding areas; US Forestry Service lists them also (e.g., George Washington National Forest in VA). www.google.com is a good search engine for this purpose.