Sleep training

Last week we started sleep training Nathan. I want him to be able to fall asleep on his own, without us rocking or swinging him to sleep. The first night was rough- he cried for one hour., but the second night he only cried for 15 minutes. Then things got messed up, as he got a late nap when he fell asleep in the car on the way home from a friends' house on Thanksgiving.
He's doing well with falling asleep at night, but he is really fighting naps. I've tried the last 3 days to get him to fall asleep on his own, but he'll cry for an hour or more without letting up. Then the nap is shot. Right now he's napping in my arms because I know if I put him down in his crib he'll wake up. I'm going to try Ferberizing him for naps again in a week or two, once I eliminate his night feedings (He is still waking up about two times a night to eat- which he really doesn't nutritionally need).