I recommend the book On Becoming Babywise. It is short, don't worry. It focuses on a good, full sleep schedule. Making sure there is a schedule during the day with plenty of rest time and plenty of nap time allows baby to sleep through the night-I know it sounds off, but a too tired baby has a hard time going to sleep. He says to get daytime down first, night will naturally follow. Do you have a good daytime schedule down?
I saw this with two of my children (one needed a little push and one I had before I read the books). Two of them were sleeping through the night by 7 weeks.
I have not ready Weissbluth's book (it was on hold forever) and it's been years since I read Baby Whisperer (scanned it last year).
My four children 8, 4 and 1 year old twins sleep through the night most of the time, it's my sanity.
BTW there are toddler sleep habit books out there-I would look for that if you want to work on your 3 year old (do the baby first). I wish I could remember the title, but I read it with newborn twins.