Training Length?

I would definitely say you could manage the sprint distance provided you are 1. in good health 2. are in relatively decent shape 3. Are comfortable with swimming and 4. have a main goal of finishing.   The Olympic distance race would be significantly more challenging for a first timer on less than 8 weeks training and unless you are already skilled at all 3 events and comfortable with a 3-4 hour effort, I'd try the sprint first.  Most people in average shape can finish a sprint and see how they do, see if they enjoy it, etc.  The only caveat is with the swimming.  Open Water swimming in a group is a totally different animal than pool swimming and anyone who is not a strong swimmer should take considerable pause before just "jumping in"

It sort of all depends where you're coming from. If you can't/haven't swam in years or haven't been on a bike since you were in Elementary school, it will be tough. If, for example, you've been running in many events and are comfortable in the water then, maybe.

I think the best thing to do get a training program:
http://www.beginnertriathlete.com/discussion/training/trainingplans-list.asp?h=1

After you look through them you'll get an idea of the training loads and see if you think it's something you can handle. No need to rush, particularly on the swim.

Good luck.

I have a friend who does 1 sprint a year (800M swim, 13mile bike, 2.8mile run) and doesn't do any training all year.
I have another friend who does the same sprint each year training all year long and there times are VERY similar.

They are obviously VERY different people and have very different skills.
As long as you are fit and feel comfortable with each of the events, there is nothing wrong with jumping in at any length, just make sure you feel comfortable with the distances and total time of the event.

Michael

Go sprint.  Better chance you'll come out with a smile on your face.