DianeL,
Obstacles. The obstacles were fairly simple. If I can recall correctly, the first obstacle was an inflatible "slide" with a rope net over it that you had to climb up and slide down the back. I the the second obstacle was a set of monkey bars. The third was up and over a rope net (no slide). The fourth was a 4' high wall that you had to vault over. The last obstacle was the infamous mud pit that you had to crawl through.
Training. I didn't do any special training for the event. If you can finish a 10k, you can finish this race. It requires an equal amount of exertion. As far as the biking part goes, just be prepared for a variety of surfaces - from sidewalks to gravel to grass to sugar sand to mowed trails. There weren't any really technically difficult areas to ride and most of the course was flat.
Adventure. I competed in the Male 56-69 combined age group with my 16 year old son. Since the race consisted of 5 legs, we decided that he would run the first leg and I would bike the first leg. The starts were separated by age/gender divisions and set to go in 5 minute increments. Our dividsion was the second start. At the start of your race, the biker takes off and the runner is released 1 minute later. At the first obstacle, the biker will get off the bike, complete the obstacle and begin running the second leg. Conversely, the runner completes the obstacle, searches for the bike, and begins riding the second leg. At the second obstacle, the roles reverse "leap frog" style. At the last obstacle, both team members have to entrer the mud pit together and then finish together.
I had a blast and look forward to doing it again next year. I may have to find another Buddy since my son has been telling all of his friends about it and will probably be teaming with one of them. Oh well, I guess I had better start convincing my 14 year old daughter to team up with Dad.
You can find official information and results/photos at the muddy buddy website. (sorry for not linking but The DIS requires a minimum number of posts before allowing the posting of URL's)