I just completed my first marathon on Saturday, after a lifetime of being overweight and the farthest thing from a runner you have ever seen. I also completed my first triathlon two weeks before that. I agree that the mental aspect of running is the toughest part. I read several books that helped me prepare mentally for the marathon. The Non-Runner's Marathon Trainer had a lot of distraction techniques that worked great for training runs, whether they were 2 or 20 miles. You might enjoy it. It has a lot of inspirational stories as well. The book suggests developing a mantra to use when things get tough. I wrote one for myself and used it repeatedly during the race. Before I read that book, I was more mentally exhausted than physically tired after a run, because I was fighting against myself to keep running. Using the distraction techniques and my mantra helped me finish strong without hitting "the wall".

I also read Triathlon 101 and have the Triathlete's Training Bible for training aids. I didn't know people who did this stuff before, and the books gave me a jumping off point. I have since met some really helpful people. Training bricks are a great help, and help you get used to going from swimming to getting directly on the bike...and starting the run after hard cycling. I thought the run was my strongest event, but my legs were tired after a hilly 25k bike ride. There are some workout schedules in there that might help give you direction in setting up your program. I knew what I wanted to do, but didn't really know how to go about getting it done. I had no idea how much swimming vs cycling vs running I needed to do. It was an eye opener.

Having said all that, crossing the finish line of the tri and the marathon were two of the most satisfying moments I have ever had. It is well worth the effort. Good luck.