This has been a question that I've been answering a lot lately. Sure, I can swim and bike and run, but what happens when I try to do them all one after the other? My guess is that it will hurt.
One of my favorite sites is Beginnertriathlete.com. A number of other beginner triathletes and some pros break down what has worked for them in training and how they get ready for a race. Basically, I take what I like and try that. The key with all endurance sports is building up your mileage in training to a heavy load, then cutting back and rebuilding. Each of the four weeks before my vacation was heavier than the last. I peaked at 116km (111km bike, 15km run), then I cut back while on vacation. So now I rebuild.
Including this week, I have four weeks before the race. This week I will go a medium distance, between 85-100km. The next two weeks will be heavier and then I will taper the mileage down on race week, to avoid fatigue.
The key to combining the events is the brick workout. Going from bike to run is brutal. But the more you do it, the more your body gets used to it. All of the training plans preach the importance of doing bricks. They are all right. I have done a few days with 20km bike rides and 5 km runs and felt okay in the end, that's practically my race mileage. Knowing how I'm going to feel coming off the bike and heading into the run gets me over a huge mental hurdle.
So can I do it?
Well I've paid the entry fee, so I don't have a choice now!