"EXHAUSTING AND EXHILARATING!"
How I did it: After the completion of P90x, my friend convinced me that I should be able to complete the Gate River Run (which is a 15K). As a test, a week before the event, I jogged 5 miles. Completing it, I felt that I could have done at least 2 more miles without stopping. With my new confidence, I decided to enter the 15K.
Lessons & tips: You should probably have the confidence. If you think you can't do it, you probably won't. I didn't need training, but that was because I had already completed a 90-day workout program. The program helped my endurance dramatically (which was obvious from the 5 mile run).
Resources: P90X. :D
It took me 7 days.
It made me WHOA!