It's stored as part of the user profile, in ~/Documents/Microsoft User Data/Office 2004 Identities/[identity, e.g., Main]. The file called "Database" or "Mailing Lists" should have it.
As far as I know, you can't extract it independently of entourage. If the Microsoft User Data folder is placed in Documents (assuming there isn't one there now), Entourage should recognize it when it starts up for the first time and load the contents.