Open Entourage. Go to Entourage > Account Settings > double-click on the account you're using with your Blackberry > in the new window that opens, go to the Options tab. Check the box for "Leave a copy of each message on the server". Now Entourage should get the mail and so should your Blackberry.
And do remember it's "Mac", not MAC. Nothing gets a Maclot (Mac zealot) riled up like this little faux pas. It might seem trivial but we Maclots are a fanatic bunch.