Rawidman and Reel Antsy,
The "Boat rental - no experience necessary" sounds rather interesting... but in regards to the initial question you can always find out state rules and regs by going to www.boat-ed.com and selecting your state. Specific to DC, we actually have a course for DC (http://www.boat-ed.com/districtofcolumbia/boating_law.html). And, it's good throughout the states.
Hope that helps!