T.A.
I am in the same boat- I have a 9 yr old son and a 4 year old daughter- I was at my wits ends with the same situation. they fight constantly over toys. I have recently put an end to it. really it was simple- I learned it off watching the super Nanny.
I sat them both down and in terms they could both understand I made the rule that fighting over toys was off limits and if they fight over a toys anymore they would go to the naughty chair. Well my son was horrified being 9 and having to go to the naughty chair and my daughter follows his steps so she hated it too! The first day they were constantly in the naughty chair and soon it became less and less and now they have stopped fighting over toys!!!
it works! try it!
T.