Also, remember, to those starting -- there is NO rule that says you HAVE to RUN..

There is NOTHING wrong with walking or doing a combo alternating walk/run!! Don't stress yourself out over having to feel that you have to run this!
I ran the Minnie 5k in 2008 - but for this last Princess 1/2 in last March, i did a walk/run combo - i walked 3 min. and ran 2.. alternating.
I can illustrate best like this : My sister broke ahead of me and my mom, she pushed herself,and wanted to see how far she could run - well, yes, she finished about 45 min. before me and my mom (i believe she finished about 2:30 - Me and my mom finished about 3:15.
Well, all she did was say how miserable she was - she didnt' take the time to "stop and smell the disney roses!" She was so intent on running. Me and my mom would chat - and take pics, and had a GREAT time -- and, we got the same medal.
So, remember, listen to your body,and just relax and have fun!!!!!
It is soooooooooooooooo worth it in the end when they put that medal on your neck --- you truly feel like a princess -- and it doesn't matter how you got across that finish line. Just that you DID.