A good bike is essential. Not sure how long it's been since you've shopped for a new ride, but todays bikes are completely different. Materials used for frames, shifting components, pedals, ect, have all changed the playing field immensely. When I made the change to a new bike, I was stunned at how much better I performed. Just be prepared to spend a "Little".
Finding the right bike is important. You can litterally shave miles/minutes off of overall times by just a bike change. Carbon fiber is the preferred material, with a Tri set up. Here is a web site for some great deals on racing/road/tri bikes;
www.fezzari.com. I've owned a Fezzari for about a year, and they are a screaming, fast bike. They will also size you up perfectly, building the bike to your exact specs. Great folks there.
I know from riding with my Tri buddy, a couple of things you should know about the cycling part; You won't be able to draft, so train out in front (if with a group) or do lots of riding alone, in the wind, climbing, and flats. Make sure you are aero (ride with elbows in, back strait, legs in, if possible a Tri Bike with aero bars). If you don't get a Tri Bike, train in the drops on a standard road bike (get low). When I ride with my friend, he likes going with me cause I make him work harder than ever.
My Tri buddy does lots of cross training (riding and swimming), which is beyond my experience. I can't even comprehend running 25-50 miles, so you'll need others to help you there. I do know he spends a lot of time running and swimming. His wife is a huge support. We have lakes here he trains in, while his wife is in a small boat to time/support him.
I'll ask my friend for some more pointers.