When do you nurse throughout the day? evening?
Your son can go to sleep at 7pm, maybe even 6:30pm if his nap has been awhile. Go through a bedtime routine before the designated bedtime- bath, jammies, (teeth), (book)- whatever you decide- make it simple! Then, feed him a FULL feeding in a dimly lit room- try to limit distractions is that is realistic- maybe get your 3 year old ready for bed at the same time and then have her read a book in her bed while you feed your son and then go tuck her in... Then, put him down in his crib and close the door. You may want to think about his sleep environment: http://www.lullabyluna.com/2008/12/happy-new-year.html.
Go get him at 7am. Of course there may be some crying as he complains about any change, but this is complaining- it doesn't mean he is hungry or hurt... He is adjusting and finding the way to soothe himself to sleep. This is a very important skill- let him have the time to discover it.
C., mother of 3, sleep consultant, sleep blog writer