Not having user privileges sounds like you may have to launch bfgminer as Administrator (just guessing) ?
I don't get the same problem with BEs.
EDIT: a bit of the log:
[2013-12-12 21:35:24] Started bfgminer 3.8.1
[2013-12-12 21:35:25] Failed to open Device Parameters registry key in lowl-vcom.c _vcom_devinfo_scan_windows__hubport():436: The system cannot find the
file specified.
[2013-12-12 21:35:25] Do not have user privileges required to open \\.\COM4
[2013-12-12 21:35:25] Do not have user privileges required to open \\.\COM4
[2013-12-12 21:35:25] No devices detected!
EDIT 2: Might be a Win 7 issue. I've now gone through the same steps on a Vista 64-bit machine, and there 32-bit version of bfgminer 3.8.1 starts hashing on BPM0
EDIT 3: Definitely something off with this particular machine. It got detected fine on another Win7 (on the second try, after pressing reset on each device).