M.B.
Hi S.- I am going through the same thing, so you have my sympathy!:) I agree with what one of the other ladies said- when my daughter starts the screaming, I just walk into the other room and tell her that we can talk once she calms down. If she really gets out of control, I send her to timeout and she will generally calm down pretty quickly. In terms of sharing, if Clare tries to take something from another child (and it's her toy) I'll take it away from her and tell her that no one can play with it if she can't share.
By the way, I recommend the Secrets of the Baby Whisperer for Toddlers (Tracy Hogg). It's a quick read and really helpful.