Need help understanding bluetooth can be used

Pardon my ignorance; but, I have just a little understanding of BlueTooth. I have bluetooth mice and I have an external keyboard for my Palm TX and Treo 680 that run on bluetooth. I also have a bluetooth ear-piece for my Treo 680; but, all of the afore mentioned are dedicated to a particular device and that is about as far as my understanding goes.

I see USB bluetooth adapters offered for sale (like these) for laptops and desktops. Does this mean I can use one of those adapters to, say, communicate with a mouse for which I lost its bluetooth adapter? Just any bluetooth mouse? Could I use that bluetooth to transfer data between my Palm TX that has bluetooth and a desktop computer?

Can you set up more than one type of device to use a single bluetooth adapter at the same time?

Thanks for your help.