You could get this from the Apple Support section for downloads, but the easiest way to get ALL updates appropriate for your secific computer is to left-click on the "apple" in the upper left corner of the screen. Then click on "Software Update". If there is an update (again specific for your computer) it will automatically download and ininstall it. If no firmware update installs then there is no firmware update you need and your solution is something else.
Not sure if this fix has already been suggested but I found resetting PRAM did the trick.
So I guess I'm coming late here but my beloved MacBook C2D late 2007 is having the same BT problems here listed. Tried everything suggested - twice - and no success. Since I used to have the MB cabled to my LCD TV in the living room I just need the BT to be working with my Apple Wireless Keyboard and Trackpad. Nothing. Shall we wait until Mountain Lion 10.8 to get this bug fixed? Or get an Apple TV, I guess...? Disappointing lack of official support here.