Rachel,
We just went through the same thing with our 10.5 month old daughter. For months she was going to sleep at 7, waking around 4 to nurse, and then going back to sleep until 7. Then in January she started waking up at 11, 1, 3 and 5. She would stand up in her crib, shake the side rail, and cry like the world was coming to an end. I was going to her each time, and I almost always ended up nursing her back to sleep. I was completely exhausted. Finally, about 2 weeks ago, we decided that it had to change. Our pediatrician recommended just not going to her and letting her cry it out, but we did not feel comfortable with that. We decided that we'd try a more gradual method of getting her back on a desirable schedule.
That night when she woke up at 11pm my husband went to her. She cried and pointed towards our bedroom (where she knew I was) but he held her, rocked her, and gently told her that it was not time to nurse. It was time to sleep. After about a half an hour he got her back to sleep. He did the same thing at 1 and at 3. When she woke up at 4:30 I nursed her back to sleep and then she slept until 7.
The next night she also woke up 4 times. My husband soothed her by rubbing her back and encouraging her to go back to sleep but he did not take her out of her crib. I nursed her around 5am again.
The next night she woke up 3 or 4 times and my husband went into her room and sang to her but did not rub her back.
The fourth night she slept straight through to 4:30 am, nursed, and went back to sleep until 7. She has now done that 9 nights in a row! My husband had a rough few nights there (though no rougher than it was for me when I was nursing her every two hours), but we are both feeling so much better now! I can't believe we waited as long as we did.
Many of our friends swear by the cry it out method described in the book Healthy Sleep Habits, Happy Child. That method is more of a "cold turkey" approach -- it may work for you.
Good luck, Rachel. I feel your pain!
S.