You basically have to reserve a room for the following year a few days/week after this year's is over. Getting one now isn't impossible, if you go thru a person and not the hotels.
Live Journal Page for DragonCon rooms
DragonCon main page
Depending what you are into, there are tons of fan tracks to follow - workshops, panel discussions, anything you can imagine. Its a lot easier on you if you decide what you want to see and attend the most, and then plan each day around that. You will not see everything. You just can't. If you have already purchased tickets, you should recieve the booklet that they publish each year with a full schedule for all events. Read thru it and you can plan accordingly. I'm not sure, but I believe it comes a month or so before the actual Con. Check online to find out about all the private parties and events - some are open, some are invite only.
If you can stay anywhere near a MARTA station, the train runs to the ARTS CENTER stop, and then you can hop off, walk around the block, and your at the main/ticket/registration area.
I know the Hyatt used to be the party spot, but they have opened up overflow hotels and such, so the Hyatt may be a little quieter these days.
I live about 30 mins. north of the downtown area, let me know if you need any help getting around. I couldn't get a room in time, so I wont be staying down there but I'll prob be there Saturday for sure and maybe Sunday.
In regards to just paying the membership fees for a pass, and driving, you should be fine, but parking could get pricey down there, especially that weekend. If you are going to be there all weekend, just get the three day pass, its cheaper than individuals.
-Mike