Ya i can totally understand.I havent been through it but my bestfriend has.

Do not let the child feel neglected at any time. Make equal amount time for all of them and deal this as one family problem.

Talk to the other child about it and involve him in the baby's work.

Sometimes it all depend on how we teach our kids about caring,loves,honesty.Parent should understand when you implement the positive influence and happiness to your children or your step-children they will be no problem to them because they know that there is no bounderies between them and new baby because they also have a feelings

however my experience has been the opposite.. one of my stepkids really really loves the baby.. but the other has been nothing but trouble since he came along. 

has your step child given any indication as to why they may have changed? 

the daughter that my husband and I share had a very difficult time with the daughter that we adopted.  she thought it was fun at first, nice to have a little sister around, but after a few weeks she asked us when the baby was gonna go back to her own mom at the time, the baby was just a foster child, so there was a real possibility of her going back to her mom, but we didn't know when.  after the adoption finalized it took a while for her to accept that the baby was not going anywhere.

with my daughter, we really made an effort to make her days special.  if she received an award at school or had done something special, we really made sure that we emphasized how proud we were of her.  we did take a couple of days here and there that were just her and mommy or daddy days, but the point we were trying to get across was that the baby was here to stay.  We could enjoy it as a larger family and no one was loved any more or less.

the baby just turned 5 and while every day is not a jubilent party, things are better.  I am hoping that what is happening now is typical sibling rivalry