The tricky part about DC driving is just sorting out the one-ways from two-ways and figuring out the roundabouts downtown. Driving AROUND DC (not just on the Beltway, either) isn't that hard, though, and you can cruise the GW Parkway to Mount Vernon, or run out to the Udvar-Hazy Air & Space museum and then up Rt. 28 to the Ferrari dealership, and then come back east on Rt. 7 to the Aston Martin dealership & Tyson's Corner.
Best bet? Fly in, rent a Mazda 6 from Hertz with a nav system, and use it to get around NoVA and Maryland (daytrip up to Gettysburg, too), but park it and Metro into DC proper.
