This is the time for you to make your stand. I have found in my short past as a nurse that if you don't put these remarks in their place then all you are going to do is build resentment toward these nurses and in the ER I think it is all about teamwork just as any other department. I relate these nurses to the bullies on the school ground, the longer you take their crap the longer they are going to dish it out. I am not saying be rude to them, but pull them aside when the chance arises, confront them and say something like, I think that was an unnessescary comment and since I am new and trying to learn here, how would you have handled the situation differently? Or something to that nature what ever would fit the situation at hand.
It is very difficult at first to deal with these types of people. Like someone else said, find an ally in the deptartment and ask advice on how she has dealt with nurses like this in the past and other things. And if confronting these co-workers doesn't work and the rudeness continues, go up the chain of command.
Sorry that you are having to deal with this, but I think all new nurses go through this to some extent. The good thing about going through this is that you know what you won't do when you are no longer the new person on the unit right??