Cool, well I propose for Saturday that we hit up downtown, we can all meet up at the D & 7th Station (Also known as the L'Enfant Plaza) at half ten (10:30am) and head from there as we'll only be a stones throw from the main run of monuments and then if we need we can hop the Metro into central for more foody type things?
From my quick reccy yesterday it's twenty-five minute walk either way down the mall (I think it's called that) to get to either the Lincon Memorial or the White House. Then it's about a 45-50 minute walk end to end. Once you head past the Washington Monument through you have to be prepared to walk everywhere as the nearest metro station seems to be the Smithsonian one.
Also I hear there is a zoo, although I couldn't find it when I looked :S
Edit: First post updated!