Hi Maggie Anne
Here is a link to the Marathon Weekend info. On the Disney Wide World of Sports you can find a course map for the races. The link I have given is to the main Marathon Weekend page. From there you can go into the Half or Full and see the COURSE MAPS located by link on the right side of the screen.
the races start at 6 am for the Half and Full.
The Half Marathon is run on Saturday, Jan 12th. It starts outside Epcot goes thru the MK and back thru the front of Epcot to finish in the parking lot. I think the last person typically finishs around 10:15 am? Somehwere in there. MK will be cleared out before guests arrive for the half, my Mom was there cheering and after the racers go thru they clear the park and clean it up
The Full Marathon is run on Sunday, Jan 13th and allows 7 hours to finish but it can take till close to 6:30 to get that last person across the finish due to the size of event and they get the full 7 hours. The parks to be affected later in the day will be MGM and Epcot and the resorts between them (Beach, Yacht area). (the Full DOES go thru all 4 parks, in 2004 we saw the Marathon for the 1st time when we arrived in the morning at AK, it was pretty kewl to see and got us started)
One thing I would ask is that everyone cross where the Cast Members are set up to help you cross. We were cheering for the Full Marathon last year and saw sooooo many people crossing at MGM and seeing near misses with strollers and runners/walkers that it was scary. By the time the racers reach MGM they had already gone 22 miles before entering MGM.
If you find yourself along the course be sure to cheer. It means the world to the racers. I know when I arrive into the MK and the crowd lining Main Street is cheering away it gives me a great boost of energy to keep going and I wish I could have time to thank each and everyone of them.
BTW, the 5K is January 11th at the AK but it's before opening so it shouldn't affect traffic or anything. And later that day is the Kids Races more info on that is on the link which is now below since I've typed so much.
I would watch your breakfast reservations and allow extra travel time for them if you make them on those 2 days.
Have a great trip!!!! And thanks for your kind words of encourgement

Oh another thing, the DIS boards has quite a large gathering of Marathon Weekend racers. You can spot them in a bright bright yellow (safety yellow LOL) shirt that says WISH on the front. So be sure to yell extra loud for your fellow board members

LOL
http://disneyworldsports.disney.go.com/dwws/en_US/marathon/listing?name=MarathonEventListingPage2
One last thing. There are points in both races that runners have to make or they get pulled off the course. Like for the Half I think the last one is Mile 10 and the Full is 20.5. I think. You have so much time to reach these set up points (they are listed in the runners race programs and in 2007 disney posted that program on the above site) and if you don't make those points they start to close the course. Disney hasn't posted the program yet but probably in November that will also give an idea of when the racers will be out of each area.