Trained for about 6 weeks and never ran before. Alternated vibrams with normal shoes. But, ran in the normal shoes to play it safe. In hindsight I would liked to have trained longer for it. I think 10-12 weeks would have worked better. I ran it in 30 minutes and had fun. Definately get a HR monitor or use some other way to pace yourself. It seemed a large number of people would take off really fast and then you would see them walking halfway through or sooner. I guess they get caught up in racing those around them. Do your first race at a comfortable pace and you will enjoy it. My next 5k is thanksgiving morning and I hope to be ready to use my vibrams.
That reminds me of a track meet I participated in when I was a kid. It was a half mile run and a black kid absolutely sprinted balls out the first lap and was crushing everybody...until he hit a wall and walked the rest of the way and finished the race dead last by far.
Was this on a street circuit or on the track?
I'm horribly unfit but used to run 5km+ in around 20min at least a couple of times a week when I was in school.