Windows Live Calendar is still not supported on BlackBerry. Or Android. Or iOS With the release of WP7 you can expect that it to remain unsupported on anything but Windows phones.
I'm not generally a fan of workarounds as they tend to suck, but perhaps syncing Dubdub's suggestion of Windows Live Calendar to Google Calendar, then setting up Google Calendar sync on your BlackBerry would be worth a shot. Windows Live Cal > Google Cal