Dan John says that the best way to motivate yourself is to sign up for an event and send in your check. I've needed to lose fat for some time now, so I figured I would do a sprint tri in August to motivate me. My goal is first and foremost to finish. I also don't want to have to rest on the swim or walk during the run.
I picked up a copy of The Triathlete's Training Bible. It's not bad. Weight training is divided into a strength phase (heavy weights, 1-5 reps) and later some endurance work (15+ reps). Keep in mind that all the swimming, running, and biking won't leave you with too much in the tank for weights. I think that Chad's Total Body Training might be a bit much. However, Chad's Triple Total Training would be almost ideal. One max strength day, one strength-endurance day, and an explosive day. The explosive day is important as this will add power to your biking and swimming, and to a lesser extent your running. Lots of tri training programs recommend plyometrics and/or explosive time moves for improving power output.
Here's a decent article on strength training for tris. It recommends lots of Olympic lifts, which is interesting. I've read a few articles here and there on tri traing and was pretty amazed at the emphasis placed on strength training. They say that it will help a lot with the biking. From my experience, that's true. I'm a fat guy with some decent strength (at least compared to most endurance athletes) and I can say that leg strength definately helps with biking. That's my favorite event and I can bike all day long. Conversely, strength helps running the least. As you would expect, my run sucks - I need some endurance big time.
The bottom line here is don't just focus your lifting on high-rep endurance work. You'll need to work on max strength and explosiveness as well.