Half Ironman Distance Training

What training do I need to compete in a Half Ironman Triathlon?

I recently did an Olympic distance triathlon and a half training just what made me almost exhausted every day. It is better to train on one leg of each day or all three together? And how do I avoid burning yourself?

http://www.beginnertriathlete.com/cms/article-detail.asp?articleid=441

2009 Whirlpool Steelhead Half Ironman