1. Hartsfield Jackson airport is about 12 miles from downtown. You can take a cab from the airport which should run you about $40. If you want to save some money, take MARTA. The MARTA train station is literally inside the airport. It costs $1 to buy a Breeze card (required) and $2.50 to get from the airport to downtown.
Other travel info at http://www.dragoncon.org/?q=transportation_resources
2. The host hotel blocks are completely booked. They literally sell out within hours of becoming available. Some of the overflow hotels still have rooms, and some are offer shuttle service to the host hotels. Atlanta is busy that weekend with other stuff going on in town so prices are usually very expensive.
Overflow hotels at http://www.dragoncon.org/?q=hotels_overflow
Or you can try your luck with the DC rooms livejournal which is the only option at this point to get the unavailable hotels. http://dragonconrooms.livejournal.com/
List is already huge with people looking for rooms though!