ooo ya, I did my second triathlon this summer with my brother, made a video and its posted on my bodyblog. (shameless plug)
First you need to decide the distance. I'd start with a Sprint, which is about 300-800 meter swim, 10-20 mile bike, and 3-5 mile run.
To finish, usually anyone can do the biking and the running part, so your going to need to get comfortable in the water. When you swim practice your form being effortless and do some long swims.
Other than that I'd just schedule the race day and do it. Prepare as much as you can but go into the race and have fun. And remember to RELAX on the swim, lol. No need to push yourself on that leg!
I have lots of other pointers but don't want to overwhelm you,