Over training during weight loss.

There really isn't an average sprint time - look at the site for the folks that are running the race and see if they have last year's results up, since that will give you the best idea.

(I did one this year that I finished in 2:05 - the winners were around 1:20-1:30 - I did another that I finished in 1:29 - the winners were under an hour.  It really depends on the course as much as anything, and it's definitely not all about distance.)

In the end though, don't worry about your time.  I did that first race as my first one ever with the goal only of not coming in last.  I didn't.  I actually finished before a dozen people.  Moreover, when I looked at my splits I was firmly middle of the pack (slight above 50%) on the swim and the bike.  My run killed me, and at 5'5" 210 I knew it would.  I'm working on it.  But not ONLY the one aspect.

You need to do things OTHER than running or you will injur yourself.  Your weight puts a lot of pressure on your joints, and while training on a treadmill helps a bit it doesn't actually stop that pressure.  Make sure you vary your workouts so that the different muscle groups have time to recover.

I would suggest changing it up so you run 2 days, bike 2 days and swim 1.  Work on your legs for your strength training on days you don't plan to run.    You have a LOT of time to both lose weight and train for this event, so try to relax a little.

I would also strongly suggest investing in a heart rate monitor and looking at the 220-Age thread.  That thread will help you set a heart rate training zone.  I can almost guarentee you are training too hard.  I did as instructed and dropped 30 seconds per mile off my running time in that zone in a matter of a month and a half.  Moreover I dropped 3 minutes per mile off my race time.  (I'm really slow - I was running a 15 minute mile, I ran 12 minute miles in my last race.) 

One last thing.  The body builds muscle and endurance by going through cycles of effort and RECOVERY.  You break down muscle fibers and then rebuild them stronger.  But only if you give your body recovery time.  Your running will improve faster if you alternate it with the bike and swimming than if it is the only thing you do because you will be providing those muscles some time to heal and build.

http://www.beginnertriathlete.com/cms/article-detail.asp?articleid=19

great article by ron - very helpful re: what you're asking

 A man after my own heart.

Yes, a HRM will help SO MUCH.  When you have a heart rate target to concentrate on it's far easier to slow down.  I used to push myself quite hard as well; I didn't realize HOW hard until I got a HRM and watched what my heart did on a normal run.  It was WAY over where it should have been.  Forcing myself to keep it down forced me to SLOW down, which in turn has drastically improved my speed and endurance.  It works.  Really.

Yes, run out and buy a heart rate monitor.  At first it seems really counter-intuitive to slow down on your run.  After all, we would all like to be faster.  I'm not sure that my pace has increased dramatically, but my endurance really took off.  I went from gasping for air and wanting to throw up after a 3 mile run, to being able to finish a 17 mile run.  Slowing down really made me fall in love with running.

You got lots of great advice already.  The only thing that I would add is that you really need to focus on the 10% rule (not increasing your mileage by more than 10% a week).  When running really clikcks, it's tempting to keep going, but that's when you're likely to get an overuse injury.

Once the weather warms up a bit, I would also suggest that you try running outdoors.  Not only does it feel different on your legs, it's much more enjoyable.  Anything above 35 or 40 degrees, and I would much rather run outside.

 Good luck on your training!

It is counterintuitive to slow down to learn to run faster, but it works. My time per mile has dropped more than 4 minutes in 9 months of training by learning to slow down my long runs. Your long runs also teach your body how to burn fat and use that as fuel. Only your muscles can burn fat so teaching them that is helpful. My 3 mile time has dropped 12-13 minutes since September of '04.

Get a HRM and listen to the advice others have given you.

I used to hate to run, but not any more I really like it and my longs runs are fabulous...time by myself, in the zone, getting fitter, and having fun!