Baby Wise works wonders. We had our 7 week old sleeping 8 hours at night. Now, a year in, we can count on one hand the number of times the baby has woken up early. She never fusses being put down to sleep. Now we give a copy of Baby Wise to every friend and family member who is having their first kid (#2+ the parents are usually too stubborn to change :-).
Update: We have three kids now. All were sleeping 8+ hours through the night within the 7-9 weeks old range.