I have a Targus acb10us Bluetooth adapter (the old version) and couldn't install it under Windows Vista until now, so in case you are having trouble too here is how I fixed it.
Go here -> http://www.broadcom.com/support/bluetooth/update.php and download the driver installer (which has been updated). I downloaded the file version 188.8.131.52.
NOTE: You’ll need to be connected to Internet to be able to install it. If you try to install it right away you'll get an error message, so before installing continue to step 2.
Right click on the file you've just downloaded and choose properties, next go to the “Compatibility” tab and check "Run this program in compatibility mode for:" and select "Windows XP (Service Pack 2)" and click on "Accept".
Double click on the installer file and that's it, you’ll be able to install your Bluetooth device, just follow the installer instructions.
I decided to write this little tutorial because I couldn't find any on the Internet, all I could find were webs from the sellers and no one included any instructions on how to install it on Windows Vista, not even Broadcom. If you are using Windows XP you won’t have any problems installing it with the included drivers, but if you are using Windows Vista don't install them because you’ll get some alerts telling you that the drivers are not safe to use, in fact I installed those old drivers by clicking like 13 times the option to ignore the warnings, and had to do a restore to bring my computer back to normal, so It’s not recommended to use the old drivers in Vista.