I bought a Kensington USB Bluetooth Adapter a while back.
Microsoft redid their bluetooth stack under WinXP SP2 to be less permissive. Kensington did not redo their adapter and its driver.
This means they have about a 2-3% chance of working together.
After calling Kensington a couple times, I elected to stop being underwhelmed by their support reps. I set out to enable the Microsoft drivers for Bluetooth all by myself.
It ended up working beautifully. If you want to do the same, here is how:
How to make the Kensington Bluetooth Dongle work with WinXP Service Pack 2 (SP2):
Don't install the kensington drivers. If you have already, go back and uninstall them (Widcom Bluetooth Software in "Add/Remove Programs").
Plug in your Kensington USB Bluetooth Dongle. Do not install the drivers off the CD when prompted.
Go into Device Manager and look under ‘Other Devices’. On the unknown device, RightClick->Properties->Details. Select "Hardware IDs" in the Dropdown.
You will see something like ’USB\VID_047d&Pid_105d’. Copy this down (or PrintScreen/mspaint it). This is your dongle's PnPID (Plug and Play Indentifier).
From the run window, open your bluetooth INF file: "notepad %windir%\inf\bth.inf". On line 170, under "Microsoft Wireless Transceiver for Bluetooth 2.0" add your USB adapter's PnPID like so:
Kensington USB Bluetooth Adapter= BthUsb,USB\VID_047d&Pid_105d
Save the file. RightClick->Uninstall the “Unknown Device” from device manager. Un-plug and re-plug the Bluetooth adapter. When prompted, let Windows search for a device driver, and it should pick up the adapter, and install the correct drivers for it. It will probably install several windows Bluetooth devices at this point.
In short: Buy it if you need bluetooth. It is cheap(~$35) because it is horribly rated. It is only horribly rated because people can't figure out how to install it. It works no worse then the $80 ones once you take 2 minutes to install it like above