In case you didn't know, you do need to restart the windows OS in the
Virtual box after adding the drivers. I am in the habit of just suspending
it and never remember to restart. If restarting doesn't work, try
suspending the OS, and going to the settings for the VM, and click on the BB
while it was connected, and click on the option to make a filter. Then
start up the VM, and restart it through start -> shutdown -> restart again.
I don't know if any of that will work, but those are steps I remember trying
before I got usb connection for my winmo phone...