The reason that your current bike wouldn't work well for a Tri is because, a Tri is meant to be a road race. At the very least, you'd need a 80's era road bike, and put on some aerobars. While slick tires would help, and you would need to get them for commuting regularly, for a Tri, it wouldn't be sufficent. (Depending on the length, it could be very short, but I don't know) Go check out the Triathalon boards, and see what they use, I'd look for an old road bike on your local Craigslist, and see what they think. Not to knock your current bike, it'll do very well for you currently. Good luck!

Edit: Found this thread, it could help with Triathlon aspirations, this is kinda what I had in mind: http://www.bikeforums.net/showthread...mber-s-example