How bout for someone who wants to be able to do the Ironman Distance, what is a good plan to follow to get into shape and follow to be able to train for a major Tri

for starting running, i am more a of a cyclist
everytime i go for a run which is once every 3 weeks, i am almost sore all over legs, my legs are totally shot afterwards
is this normal, so do i need to run more to override this