Sibling rivalry already?!

Our 5 year old has just started Kindergarten this week and our 2 1/2 year old has just started this week being very vocal and adding to the rivalry between them when she is home. I am thinking he is feeling a little topsy turvy with her being gone in the mornings. It is a strange week for both of them and for us. What do you do when you can't stand the whining, arguing, screaming, etc that they do when they are "playing" in the living room? I separate them and put them in different time out areas and have to repeat that over and over. I try to tell my oldest that she should be the big sister. I know it is hard for them both to adjust to this new schedule. Any advice on how to get them to play better together would be great........my hair will be turning white shortly if this continues.....:)