J.R.
My two year old did something very similiar- but not until the baby was actually here. She tried to jump onhis head, would act out like you described as soon as I was nursing him. It was hard, because she is typicaly very well behave. In our situtaion I found that we were giving her negative attention- which was what it was about-- she wanted attention no matter how she got it. So we set up a merit board with the rules of the house and rewarded her with stars whenever she did soemthing good, the rules were done in pictures and we would go over them (things like sharing with others, giving hugs and kisses not hits, putting toys away when done, and using her manners). It was a strain the first couple of days- I was literally coaxing her into doing the good behaviors so that I could reward her, and if she broke a rule we took a star away, whenever she got to five stars she got to pick a sticker or have a piece of candy. She caught on pretty quick and start wanting to act good because we made such a big deal out of it..... and when she was bad it was very simple- we take a star away and move on--- so she didn't get the attention from acting out-unless she hit then she got a star taken away and a time out. Also, maybe relax on your talk about the baby-- she knows its coming.. try and spend as much 1:1 time with her as you can now-- because it is really hard once the new baby is here to do it. When our son was born I bought a baby doll and had it wrapped up at the hospital for her-- told her it was from him-- and then encouraged her to take car of her baby when I was taking care of mine-- this didn't work with her-- but I have friends whose daughters loved this. Be consistent and be patient this is a transition for her. It took a while, about six weeks, before our daughter was really herself again-- he is now four months old and she plays with him, and trys to love on him.. so it did get better for us.. Good luck and congrats on that new little baby!