I built my fit PC3 with Win7 as descibed here.
I have an old Microsoft Wireless Optical Desktop for Bluetooth Keyboard and a Microsoft IntelliMouse Explorer for Bluetooth. Immediately after installing Windows 7, I paired up the keyboard and mouse using the built in Bluetooth (rather than the dongle that came with them) and the standard OS drivers. Both worked. Then I installed the fit-PC3 Bluetooth package. After that, neither device worked. I re-paired the keyboard - the app displayed and accepted the pairing code but after that nothing that I typed would appear. For the mouse, it asked me to enter a pairing code: rather tricky when you've only got two buttons! I tried morse code but it didn't seem to work.
I uninstalled the Bluetooth package but couldn't get the OS drivers to work again. Running out of play-time, I rebuilt the device and this time I didn't install the Bluetooth package. Both devices are working again.