Hi Stacy
Some people go from c25k to the One Hour Runner program. It can be found here:
http://www.coolrunning.com/major/97/training/swit0214.htm#run
After I finished c25k, I just kind of slouched around, ran another 5K, and tried to get my mileage base up, working my way slowly up to an hour. Since I got to that point, I've just been inching up, running about 3 times a week with two 3-4 mile runs and one longer run that I have increased the distance on pretty gradually.
There are lots of training programs for sale out there on the web, but runnersworld.com has a virtual trainer program called "Smart Coach" that will churn out a personalized training plan based on the event, your current level and weeks available to train, though they aren't as geared for the absolute novice who happens to have a few miles under her belt (such as myself!) and I didn't really follow it in training for the ToT race.

These seem to me to be more for people who are trying to get a certain speed rather than people (such as myself!) who just want to finish the whole thing.
I second the suggestion of looking in the Marathons for Mortals book - surprisingly, he does have training plans for other distances in there, if I am recalling correctly.