Get the free Funambol SyncML client from:
Use the desktop tools from Blackberry to install the application. You'll find the application in the Menu -> Downloads section on the device. We tested 8.7.1 on OS 4.6 successfully with notes, contacts, events and tasks.
You'll need the following information to setup the application.
SyncML server URL: http://<Enter the URL for your Group-Office>/sync.php (Look it up at Settings -> Synchronization in your Group-Office)
Username: Your Group-Office username
Password: Your Group-Office password
The default settings should work but if something goes wrong check the advanced settings of each datastore: