Don't drive in DC, it'll take you longer to find a parking space than to get to where you're heading. It's no big deal to drive to the places outside the city, but note that traffic in this area can be horrendous so ask about what direction you're travelling in and at what time of day (avoid rush hour) with the hotel staff before you take off. You'll have two people in the car so you will have access to HOV (high occupancy vehicle) lanes, if you happen to be driving in the appropriate direction at the right time of the day.

This thread may help some: http://www.flyertalk.com/forum/showt...4&page=1&pp=20