The last - and hardest - part. Main things to train are: for the shorter races (usually 10k, less for sprint distance) ability to run off the bike, which is done by adding a short run to your long or hard rides. For the longest distance (42k for the full Ironman), you would also need to increase one weekly run gradually to the point where  you are doing up to a three hour run, one month before the competition.
There are a lot of great books on running. My favourite is Tim Noakes' "The Lore Of Running" which is about the most complete book possible on the subject, but if you don't feel you can handle something that heavy,   
Chi Running" by Danny Dreyer is an excellent way to develop a very natural and relaxed running style.
Run
Training
Triathlon main
Hosted by www.Geocities.ws

1