I TOTALLY agree with Heidi. However, I'll tell you that my child was trained differently. He was reluctant to poop in the toilet. He occasionally would pee in there, but that was not consistent, either. One day, he'd taken off his wet diaper and smashed it on the floor, sending those little gels all over my freshly scrubbed floor.
I took his diaper away and told him that if this is how he acts in diapers, then he can't have them anymore. I handed him a pair of underwear, told him to put them on, and made him clean up the mess. That was it. Over a year of begging, coercion, bribery...and just telling him "that's it" was all it took.
There is another method that a gastroenterologist does (and will guide you through for only $450). Put a TV, books, and toys in the bathroom, put the kid in ONLY a tee shirt, give the child Miralax, and spend 72 hours in the bathroom with the child (sleeping in there, too). He says that by age 4, it's all about control, and that the child WILL be using the toilet at the end of this period, and will be "trained" at the end of 96 hours. Honestly, his method makes sense to me-if the child has no choice but the toilet, and nowhere to hide to poop behind the couch or whereever, he'll learn to use the toilet. Here's a link to his page:
http://doctordaum.com/