Hi and welcome to the forum
You do not need to install any new permanent hardware drivers
in Windows XP mode (RAM, Graphics etc) because Windows XP mode is designed to run inside Windows 7. You do however have to install extra drivers for peripheral hardware such as your USB Bluetooth dongle.
If you plan on using a USB Bluetooth dongle with XP Mode it really couldn't be much simpler.
Open Windows XP mode so you have the Windows XP desktop in front of you in a window and make sure Virtual PC Integration components is installed (it will have installed automatically the first time you set up XP mode).
Plug in the USB device you want to use in XP Mode.
Go to the USB menu near the top of the Window and select the device you have just plugged in.
It may now ask you to install the appropriate drivers for your dongle, follow what it says on screen and have the driver
Hey presto you're done
I hope this helps, if you have any questions feel free to ask them.