My baby girl slept through the night for the first time just last night. She is almost seven months. We've been slowly working at it for over a month. Be sure to have a CONSISTANT bedtime ritual. I cannot stress this enough. We have bathtime, lotion massage, maybe a story depending on how tired she is, nurse her, and then stand up with her in the nursing position but with a pacifier in her mouth for a couple of minutes but don't let her fall asleep and then put her in her crib. I say "time to go to sleep, I love you" and walk out of the room.
This is the critical part.She will almost always start crying. I let her cry for 5 min, then go back and tell her I'm near, put her pacifier back in (this will be the next habit to tackle so if you aren't using a pacifier just ignore this), maybe touch her belly but do not pick her up, and then walk out of the room again. She'll probably be crying still but don't go back in there for ten more minutes. Keep extending the time period by five minutes. She'll feel safe and know that you are near and eventually fall asleep. You have to do this every time she wakes up in the middle of the night so it's usually best to start on a friday night or you'll have a very tired week. If the dad is able to have him help as much as possible because your baby can sense you and wants you to pick him/her up.
The reason it took us over a month is because I was only increase the minutes by like 2-3 in between going in there so I'd go in there at 5 min, 7 more min, 10 min after that, 13... but it works! For my friends (I live on a military base.. lots of friends with babies), who actually wait the full 5 minute incraments say it only takes about 3-4 nights to work! CRAZY! GOOD LUCK!