Is there a software / driver which will allow my Windows PC to "emulate" bluetooth keyboard so that I can control a tablet or other device just as if I was using a dedicated bluetooth keyboard?
I found a possible solution for linux here http/anselm.hoffmeister.be/computer/hidclient/index.html.en
If you're really determined, you could probably set up a linux virtual machine in virtualbox or something, plug in a bluetooth dongle and tell virtualbox to connect it through to the linux VM, and then run the HID emulator in there. Alternatively, there's source code, so it might be possible to adapt it for windows (don't hold your breath)