Backup files are not designed to be opened at all. They're designed for restoring after wiping a BlackBerry or after changing devices. To access your information on your BlackBerry via computer you are expected to sync it with Outlook or some other program(s).
Microsoft now makes Outlook for Mac: Outlook for Mac : Email, Contact and Information Manager | Office For Mac
I don't know if BlackBerry Desktop Software supports syncing to the Mac version though. There should be a way to sync your BlackBerry contacts with AddressBook.app on your Mac. It's been so long since I've used a BB7 device that I really don't remember how.
There is an old discussion on CrackBerry about this, highlighting some issues folks have: http://forums.crackberry.com/mac-use...s-book-387367/