I couldn't run that far if my life depended on it :D We had two runners on Saturday and one person made it the whole way and the other elected to ride the last approx 6kms.
I bike my dogs 3 times a week and slowly increase the amount of kilometres I do and also make sure to use all the different surfaces required, swim them fortnightly and walk about 10kms each day (not on the days we bike) with lots of free running to keep their endurance levels up.
Sounds like your dog will have no problems with the distance if you both jog together regularly. Good luck and let us know how you go :p
Thanks for the advice wolfgirl. I've just come down with a flu/sore throat so that stuffs my run training for a few days! And my running partner (who was also going to enter her dog) is having second thoughts, so I may not be ready in 6 weeks after all. I'll see how the next couple of weeks go before I commit.