I have recently been trying to get a bh200 head set working with a new installation of Windows 7 on an old XPS M1530.
After trying various Widcomm drivers without success I stumbled on a post on the Dell support forums which seems to solve the problem with the following steps:
1.You need to force Windows 7 to detect the bluetooth module, so download the Dell patch: R159805
2.At this time, the bluetooth module should be detected and installed by Windows 7
3.Go to Dell support and download the latest driver for the bluetooth module (for Dell XPS 1530): R140135
4.Install the driver. It will update the module's firmware