I just want to second Mothering Your Nursing Toddler. What a great book. I did nurse through the early months of my preg (my ds was just turning 2) but he was weaning slowly anyway and the decrease in milk supply by about the 5th month did him in. There is a HUGE section in there on tandem nursing. The thing that it great about the book, I think, is that it gives you permission to feel all the different feelings you may encounter, from restlessness and resentment during nursing sessions with your toddler (this happened to me in the pg) to the joys and wonder and benefits of continuing to nurse. It doesn't say you have to do anything either way, KWIM, but reading on paper the things that you are feeling is a huge relief (at least it was for me) and the same thing happened when ds was like a little over a year, he was nursing like a little zealot and I felt burned out. The book was very helpful at that point too.
HTH and congrats on your pg.