I'll have to disagree with Mrrzy and Bobert, with respect. I am a native Washingtonian. I have never known a cab driver to be unfair in our city. It's not impossible, but not likely. Out Metro is clean and efficient and well-marked, reaching all the parts of the city. One stop, The Smithsonian, will put you in the middle of all the best museums and many of the best gallerys, as well as the Capital, Monuments, etc. For your hotel the Metro is far and away your best bet. Arlington Cemetery has it's own metro stop. See my link above. I assume from above you're training for the marathon? You will be one block from running through the zoo and down through Rock creek park, where parts are closed for runners and roller bladers on weekends. I'll be running down there with you.