Hi Ashlyn! You have made a great decision! RunDisney races are so much fun!
I am assuming that you mean the Disney World half marathon that takes place in Orlando, FL on January 12, 2013. There is also a Disneyland half marathon in California that takes place Labor Day weekend, but it is already full for this year.
For the Disney World half marathon, you should register as soon as you decide for sure that you want to do it. It isn't getting close to capacity right now, but it does usually fill up before race day. Registering will also make it "official" and will kick-start your motivation to begin serious training for it.
Once you register, you will also have access to runner's discounts for rooms, theme park tickets, etc. You will receive a password and number to call in your confirmation email to get your discount. I do recommend staying at a Disney resort. They will have buses going to and from all race weekend activities. Because of road closures and heavy traffic, the buses are a huge relief on race morning.
You can find all of the information on the
Disney World Marathon website. Just click on "event overview" and then "Disney World Half Marathon".
Registration is now open and you can book resorts now too. Let me know if you have any other questions as you begin planning for your Disney World half marathon!