yea, 2400 M St is legit. Dupont south is pretty close to foggy bottom and McPherson (the Flats is about a ten minute walk to the foggy bottom metro. Unfortunately, most of the pet friendly places are a little pricey (approximately 1700 for studios). While you probably cannot get a short term lease from the management company at either, you may be able to get a sublet off of craigslist. Also, Nalp puts out an apartment exchange listing service soon (not sure when, I just remember getting some sort of email).
If you have any questions about neighborhoods, etc, ive lived in NW DC for about 3 years now and would be happy to provide any insight I have.