What distance are you going for?
When is your race?
What are your goals?
What's your current level of fitness?
In terms of books, people always sight Triathletes Training Bible by Joe Friel as the best book out there, but it's pretty technical and imo geared more towards pro level athletes. However, there is a lot of great information.
SERIOUS Training for Serious Athletes by Rob Sleamaker is what I'd buy if I only got one book.
Total Immersion is great... I'd also suggest searching out your city's Masters Swim Team.
Most newbies make the mistake of increasing distance too fast. Distance in any sport shouldn't be increased more than 10% a week. Training for a sprint distance tri can be easily done with one sport a day. Longer distances generally require 2 workouts a day. (Though some claim 1 long workout a week for each sport is all you need... 2 swimming, 2 hours biking, 2 hours swimming... like everything else you gotta find what works for you.)
I train 2 x day 6 days a week with 3 days of weights. My weight training is periodized to synch with my sport specific training. It's winter so my "cardio" sessions are LSD (Long Slow Distance) swims/rides/runs and weights are in the endurance phase - 50% 1 rep max at high rep.
good luck!