The most important thing is to just get in the water and swim. Also do some reading on swimming technique. Swimming is 99% feeling comfortable in the water and moving efficiently. Before I did my first tri this summer, it had been a LONG time since I had been in a pool, and had never truly swam any distance before. My first swim workout, I nearly gave up the idea of doing a tri on the spot because I could barely do a length of the pool. By my 4th swim workout I was doing a couple hundred yards at a time and had much improved. A good place to check out is
www.trinewbies.com... check out their "getting started" section. Also there's a great book for beginning triathletes by Eric Harr. Its definitely worth the money. Keep reviewing the swim techniques in between each swim workout you do and each time you go out focus on one or two aspects of your technique and make sure you get those portions right. Don't get frustrated by the difficulty of swimming early on... it'll come to you.
If you have more questions, post 'em, or feel free to PM me.
