There is an "official" Tough Mudder training program, prepared by the Tough Mudder folks. You could start here. They've posted a selection of different workouts for the following levels of fitness... mudderling.... maybe mudder.... tough mudder.
Start at the beginning and see how you do. I did a Spartan Sprint and I found some of their training workouts just a wee bit over the top. So, I did skip those.
One thing I would suggest is starting a good strength training program to start increasing your over all strength.
Don't worry... Tough Mudders are all about teamwork. everyone helps each other out when it comes to the obstacles. toughmudder.com/training-prep/
Edited by: ARCHIMEDESII at: 1/9/2013 (14:55)