Recently I had a user install a new Bluetooth device to his Windows Vista laptop which somehow corrupted the drivers for his Blackberry handheld. This user often uses his Blackberry as a modem when WiFi or other Internet connection is not available. He uses the laptop and Blackberry's Bluetooth to establish the connection between devices. The problem was each time he would boot his laptop or connect the device with a USB cable, it would prompt for a driver installation. The driver installation would ultimately fail and the device manager would show two "Unknown Devices".
After many attempts of uninstalling the drivers, reinstalling Blackberry Desktop Manager, the AT&T connection manager, and directing the installer to the drivers in the Common Files directory, they simply would not install. The solution was to manually choose the drivers by choosing from a list of device drivers on the computer.
Open Device Manager
Right click on the Unknown Devices and choose Update Driver Software
Choose "Browse My Computer for Driver Software"
Choose "Let me pick from a list of device drivers on my computer"
Select "Ports LPT & COM"'
Under manufacturer select "RIM Virtual Serial Ports"
Choose the only driver "RIM Virtual Serial Port v2"
Apply and it will successfully install. Do the same for the other unknown device and the Blackberry should now work without any future prompts.