I've just started training for my first Tri in May -- a sprint triathlon. I've been mountain biking a few times a week, and run an occasional 5K.
I plan on buying a road bike here pretty soon -- will probably get a used one on Craigslist or something, but there are some on bikesdirect.com that look tempting.
I grew up swimming, but distance swimming in open water is a whole different beast. I did a bit in a nearby lake this fall, and it kicked my butt. Will be focusing on that for sure -- luckily our gym has a pool.
I'm anxious to hear any more advice for a first timer. I've been checking out BeginnerTriathlete.com - Triathlon Training for Beginners
for some training tips.