I was wondering if it is possible to use a bluetooth headset, which is paired to a blackberry device and while having the phone sync'd to a pc via usb, and use this setup to chat through the headset on programs like messenger and multiplayer games?

If that is unclear,
is it possible to use a blackberry and usb cable as a bluetooth adapter?

I don't think it will work. At least I have not heard of such a set up.